FAQ BREAK DOWN
Engine info
Acronyms
Vag diagram
Common part numbers
Basic Mods
1.8T Trouble shooting guide
Helpful links/how to's


Models: 180, 225, and 250hp

TTENGINE INFO

-06A Block: internal water pump
-DOHC engine (only exhaust cam gets a cam gear)
-All heads are small port and can be swapped to big port AEB heads. Will need big port manifold or spacer from 034motorsport
-Displacement: 1.8L (1781cc)
-Firing Order: 1-3-4-2
-Cylinder #1 is next to the timing belt
-catbacks are 2.17" 180 and ~2.5 crush bent on 225's
-Oil Capacity: 4.6qt (4.35L) ~5qts with a big A4/passat filter
-Head bolt size: 10mm
-Engine Mount Assembly/Mounting Info

Engine dimensions for OE engines:
Bore size - 81mm (3.19in)
Stroke - 86.4mm (3.40in)
Rod Length - 144mm


HALDEX

A swedish company that built the TT/R32 awd system. The differnce between a TT and other awd systems is thata % ofpower is transfered from the front to the rear when needed. On the highway the TT is basically a FWD car and will gain better mpg. When the car senses slip or an increase in power, the haldex will send power to the rear (from 10-50%) for better traction. This can happen as fast as 1/32 of a tire rotation. This is also the reason why dynoing a TT on a awd dyno gets bad readings. Since the power is constantly changing, it throws off the dynos reading. You can however dyno the car in fwd by pulling a fuse and then reinstalling it when done. It can be bad to drive the car for a prolonged period of time with the fuse pulled and not advised by Haldex.



ENGINE CODE 1.8T

HEAD




BLOCK




180HP MODEL


Curb weight coupe 2910 (fwd), 3131 (awd) varies per website
Curb weight roadster 3054lbs(fwd),
Available from 2000+ in both FWD (00+), AWD (00-03), and tiptronic and fwd (04+)
5sp with a 02J (212mm) in the FWD and 02M inall AWD models(240mm).
- The fwd upgrade use a G60 flywheel and VR6 clutch (228mm).
2.75" Maf O.D.
Single cat for fwd, twin cats for all awd models
single tip exhaust, AWD cars can use 225 catbacks (will need a 225 valance).
intake manifold faces the passenger side and uses a single smic
Fuel injectors - 317cc @3bar


Engine Code: ATC
Model Years: 2000
Compression Ratio: 9.5:1
Horsepower (SAE Net): 180hp @ 5500RPM
Torque: 170ft. lbs.@ 1750RPM
ECU: Motronic ME7.5
DP Size: 55mm (2.17")
Turbo: K03
OE Boost: .8 Bar (11.6psi)

Also comes with 16v rods with 20mm wrist pins. These are stonger than the new 19mm wrist pin rods and will hold 310-325wtq (tq breaks rods, not hp).
The ecu is smaller and chips most often are soldered on.
uses narrowband o2(nbo2) sensors to control the ecu pre and post cat.
Is nonVVT

Engine Code: AWP
Model Years: 2001+
Compression Ratio: 9.5:1
Horsepower (SAE Net): 180hp @ 5500RPM
Torque: 174ft. lbs.@ 1950RPM
ECU: Motronic ME7.5
DP Size: 50mm (1.97")
Turbo: K03s
OE Boost: .8 Bar (11.6psi)

Uses 19mm wrist pin rods. Good for about 300-310wtq.
larger ecu momory size, chips are flased on.
uses a wbo2 (wideband o2) and controls a/f ratios better, results in better tunes.
has VVT and is only used at start up for emissions.

225HP MODEL

Curb weight 3208lbscoupe(varies per website)
Curb weight 3362lbs roadster
02M 6sp tranny
16v 20mm wrist pin rods.
Maf 3" O.D.
Intake manifold with drivers side throttle body.
Uses twin smics
Uses twin cat set up
comes standerd with dual exhaust
fuel injectors - 386cc @3bar

Engine Code: AMU
Model Years: 2001-early '03
Compression Ratio: 9:1
Horsepower (SAE Net): 225hp @ 5900RPM
Torque: 207ft. lbs.@ 2200-5500RPM
ECU: Motronic ME7.5
Turbo: K04-20
OE Boost:1 Bar (14.7psi)

Still uses nbo2 to control a/f and has smaller ecu.
still uses nonVVT

Engine Code: BEA
Model Years: 2003+
Compression Ratio: 9:1
Horsepower (SAE Net): 225hp @ 5900RPM
Torque: 207ft. lbs.@ 2200-5500RPM
ECU: Motronic ME7.5
Turbo: K04-22/23
OE Boost:1 Bar (14.7psi)

Uses a wbo2 to control a/f ratios and has larger ecu
comes with VVT

Other basic info can be found here

250HP VR6 3.2

Displancement 3189cc
Dohc
compression ratio 11.3:1
hp - 250 @6300
tq - 236 @2500
curb weight - 3424

more info here


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SPARKS PLUGS
OE Plugs: NGK PFR6Q - .032" gap

For Stock Cars - .032" gap:
NGK BKR6E
Autolite 3923
Denso Iridium IK20

For Chiped Cars - .028" gap:
NGK BKR7E
Autolite 3922
Denso Iridium IK22


**Avoid all non copper plugs, recommend to change every or every other oil change to keep from misfiring.
General Rule of thumb: For every additional 50HP over stock, a general rule is 1 heat range colder and gap shrinks by .004
--So, a chipped 1.8T would make good use of a plug one range colder gapped to .028 but can use stock heat range if mildly tuned with chip and turboback.
>Tightening torque 30Nm (22 ft-lb)
>Tightening torque for Coil Packs 7ft lbs

Oils
502 or 505rated oils. However some oils like Royal Purple do not send their oils out to get tested for ratings, they have more than proven themselves on the 1.8T engine.

Complete list of approved oils here


What is VVT?
VCT or Variable Cam Timing. Synonymous with Variable Valve Timing. The VCT in later 1.8T's is simply for emissions purposes. It has only two states - normal and massive overlap. The overlap is used to draw exhaust gasses back into the cylinders at startup.

Coolant
All engine MUST use G12 or G12+ coolant. Also, refrain from mixing in other coolants and additives since they can either eat away the radiator or turn the coolant into sludge.

 

ACRONYMS

IAT - intake air temps. There is a sensor in the intake manifold that can be view via vagcom
SMIC- side mount intercooler
FMIC- front mount intercooler
IC- intercooler
CAI- cold air intake
SAI- secondary air injection. Used on cold starts to warm engine and cat faster.
CTS- coolant temp sensor.
DV - diverter valve
BOV- blow off valve
BBK- big brake kit
BT- big turbo
MAP- manifold absolute pressure. Speed density sensor in stock ic
MAF- mass air flow. Air flow meter attached to the airbox
MBC- manual boost controller.
EBC- electronic boost controller
n75 - stock boost controller. It is non adjustable and in the intake behind the maf
PCV- positive crankcase ventilation. Main cause of oil in intake and ic.
TB- either throttle body or timing belt. based on context
TIP- turbo inlet pipe. piece from the maf to the turbo
w/m or wmi - water/meth injection aka alky injection
DBW- drive by wire. electronic tb
DBW- drive by cable.cable operated tb, not used on the TT but is needed if you go stand alone ems
EMS- engine management system
SEM- stand alone engine management


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VAC DIAGRAM







Turbocharging System, Overview
1 - Vent line

From gravity valve at fuel tank.
2 - EVAP canister

With Evaporative Emission (EVAP) canister purge regulator valve -N80-
3 - Turbocharger
4 - Check-valve

For EVAP canister system
5 - Pressure unit

For Boost Pressure Regulation Valve
6 - Deceleration shut-off valve
7 - Wastegate bypass regulator valve - N75

Valve is activated (pulsed) by the Engine Control Module (ECM)
Checking activation: See Output Diagnostic Test Mode (DTM), activating. Refer to "On Board Diagnostic". See: Computers and Control Systems\Testing and Inspection
8 - Brake booster
9 - Check-valve

For brake booster
10 - Air filter with Mass Air Flow (MAF) sensor - G70 -
11 - Pressure control valve for crankshaft housing ventilation
12 - Combination valve

For Secondary Air Injection (AIR) system
13 - Fuel pressure regulator
14 - Check-valve
15 - Recirculating valve for turbocharger -N249-
16 - Secondary Air Injection (AIR) solenoid valve -N112-
17 - Crankcase ventilation
18 - Check-valve

For EVAP canister system
19 - Charge air pressure sensor -G31- / charge air cooler
20 - Secondary Air Injection (AIR) pump motor - V101 - *

Checking function. See: Emission Control Systems\Air Injection Pump\Testing and Inspection
21 - Vacuum reservoir


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COMMON PART NUMBERS


Engine

PCV Parts - Suction Pump: pn 058 133 753 b (image)[*]PCV Valve: pn 035 103 245 A (image)[*]PCV Hose (V-shapped connects valve cover, lower breather port and intake): pn 06A 103 221 BH (image)[*]PCV Hose (from lower crank case vent to Y shaped hose) pn 06A 103 213 AF [/ul]
Fuel Injectors - 06A 906 031 S (AWD/AWP, 317.46cc/min@45psi, 369cc/min@60psi)[/ul]
Coilpacks - 06B 905 115E (AWD - Bolt Down) 06B 905 115R (AWW/AWP)
OE Oil Filters 06a 115 561 B Transverse Oil Filter 068 115 561 B Longitudinal Oil Filter (larger one specified by TSB, usable on the transverse motors)

Gaskets

Head Gaskets: European 83mm bore - 06A 103 383 AF [/ul]
Intake Manifold Parts 06B 133 555 H (Injector Seat)[*]06A 906 149 Injector Seal O-rings (set of 4)[*]058 129 717 D Intake Manifold Gasket

Sensors

Mass AirFlow sensor (MAF) 06A 906 461 A (for 2.0, but seems to work with AWD) 06A 906 461 D (AWD/AWW)[*]06A 906 461 L (AWP) Latest revision is LX
MAP Sensor 038 906 051 Large[*]038 906 051 B Small
Air Temp Sensor 00-03 (including 337) 0 280 130 085 03+ 06N 905 379A
N80 Purge Valve
0 280 142 354
Y pipe under intake manifold (AWD?)
058 133 753B

Cam Chain Adjuster
058 109 088 E (List is ~$700!)

Diverter Valve
06A 145 710 N (TT/NB Turbo S)

N249 (Diverter Valve Selenoid)
028 906 283N (NB Turbo S/???)

4.0 bar Fuel pressure Regulator
078 133 534 C

Head Bolts
06A 103 385 A (AWD, APH)

Exhaust Manifold Gasket
058 253 039 G

Coilpack Replacement Harness
1J0 971 658 L

Transmission
VW "High-Performance" 75W/90 Transmission Fluid
G 005 100 A1

02J 2nd gear grind fix ... parts off "moclov"'s invoice:
[2] - G-005-100-A1 - oil, .5 litr
[1] - 00076 - brake klee
[1] - 02J-311-239-J - synchr hub
[2] - 02J-311-247-C - synchr ring
[1] - 02J-311-261-K - 2nd gear
[1] - AMV-188-200-03 - seal comp
[3] - G-005-100-A1 - oil, .5 litr
02M 2nd gear grind fix ... parts off "genxguy"'s invoice:
[1] - 02J-311-251-J 1st gear
[1] - 02J-311-261-L 2nd gear
[1] - 02J-311-239-J synchr hub
[2] - 02J-311-247-C synchr rng
[2] - 02J-311-277-A synch ring
[2] - 02J-311-279 Outer ring
[1] - 02A-311-531-K reversgear
[2] - G-005-000 Oil-1 litr

 

Basic Mods


CHIP
Increses both boost and timing to give a substantial gain (see tuners' website for claim).
Popular tuners - GIAC, APR, Unitronics, REVO, and Nuespeed.
- please aviod upsolute, eip, and any budget chips.

DIODE
For those w/o the money for a chip or plan to upgrade turbos sooner than later, a diode is a simple upgrade to increase boost. The diode limits the voltage from the map to the ecu and prevents the ecu from going into limp mode (5psi) for passing 1bar. The o2 and maf will make up the fuel for the increased air. How to and more explaination here.

DV/BOV
After the increase in power, it is a good idea to also upgrade the stock dv. The 225's 710n is a rather durable dv and should withstand a good deal of power. Only problem is that like all diaphrams, it can wear out or tear. A piston valve doesnt work as fast but is tunable and far more durable. There are good diaphrams available such as those from apr and hyperboost.
good valves: forge007, apr R1, hyperboost, turboxs h25, greddy, hks.

Bovs are ok to use on the car, but not all cars will accept them with stock power. To use them, you MUST have a valve that is closed at idle. These include a twin piston valve and a HKS ssqv. This prevents thecar from stalling and leaking air at idle. It will also not run rich after the car adapts (sometimes not needed to at most 2 days). The best bovs are the forge004 and ssqv. For BT applications, a tial 50mm bov.

DOWNPIPE
A downpipe is probably the next biggest gain after a chip. It frees up the exhaust flow and makes great power.
- 225- 42dd dp or apr with full turboback.
- 180q - tCarbon and 42dd either do or will have dps available (no, a 225 dp doesnt fit)
- 180fwd - any VW 1.8t will fit. Ebay dps are cheap and fit well.

CATBACK
Great way to finish off the exhaust. A 2.5" is the min and 3" max for all 1.8t's.
A 225 catback will fit on a 180q car.
there is no good way to make a fwd have dual exhaust, but miltek has a kit availble

INTERCOOLERS
FMIC's will cool the increase in heat from the turbo when the car is chipped. In the summer time the car could use an upgrade.

TIP
a turbo inlet pipe willsmooth the airflow to the turbo. The 225 sometimes has a problem with it collapsing since it is all hose. The upgraded hose will prevent that. The 180 will have a smoother path since the cast peice has a smaller 90* bend.

INTAKE
Not a real gain here. You will see a change in throttle response, but no real hp gain. Just remember that on a turbo car, flow matters and temp not much. Get the best flowing intake as possible.

SUSPENSION
springs/shocks or coilovers. Both are a great upgrades. The main differnce is the coilovers can adjust ride height where springs cant. Always replace the shocks with performance koni/bilstein since the stocks will die fast and the newer shocks will give a better ride.

SWAYBARS
Another great and often overlooked part. By adding/increasing the diam or the rear sway bar, you will gain a more nuetral car if not gain some oversteer. Just take into account that if you plan on doing both front and rear, they need to work together. Its best to stick with the same brand since they are made to work together.

BRAKES
With amildy modded car (chip and bolt ons) just a simple upgrade in pads will help greatly. With more power it is recommended that you increase the brakes further with a BBK.
brake basics:
- solid rotors - simply a solid metal rotor
- vented rotors - have vanes between the front and back of the rotor to vent heat out of the rotor
- plain - have a smooth face
- slotted - have channels cut in the rotor. Cleans the pads and lets gas escape.
- cross drilled - have holes in the face to push water and gas off the pad/rotor.
- 2 peice - have a aluminum hats on a zinc rotor. Cools faster and removes a good deal of weight

however the xdrilled and slotted rotors look nice, they actually remove surface for the pads to make contact with the rotors. Its best to have a plain face for just a mild street car. Also avoid buying xdrilled rotors from a non name source. Even if they use name brand rotors, doenst mean those are the people that drilled the holes. These are known to crack easy when the heat is to much.

HALDEX CONTROLLERS
Those with quattro can get a controller that improves how fast the power is sent to the rear and how much. Not really going to see a huge unpgrade on the street except on launches. Best if used on cars that are tracked. You have 2 choices, a blue and orange. The blue is more mild and recommended for street cars since it disengages the rears when braking and the orange does not.

WATER/METH INJECTION
A little more advanced but can make a significant improvement on the stock turbo. It basically lowers the iat (water) and increases the octane level (meth). This allows you to increase boost/timing to gain power. To take full advantage of this you will need both a vag com cable (ross-tech.com) and unisettings (from unitronic). Other benifits are it reduces knock and cleans the cylinders. For more info, use the search feature.

WHEELS/TIRES
a commonly over looked part. Lighter wheels and stickier tireswill make the car go faster due to less unsprung weight. Also the tires will stop the car much faster.

WEIGHT REDUCTION
a simple and ofter free mod. Less weight = less to get moving. This can increase 1/4 times (100lbs lost = .1 sec) and mpg. Just dont remove anything safty related than can cause harm when removed: ie crash bar. Cleaning out the engine bay


COMPLETE IDIOTS GUIDE TO MODDING A 1.8T

STOCK TURBO TUNING GUIDE

 

1.8T Troubleshooting Guide.

Section 1. - Symptom - Possible Problem Parts (in order of likelihood)
Section 2. - Part Troubleshooting Method - Alphabetical


Section 1.
Rough Running At Idle - MAF, Ignition Coil, Spark Plug, VAC Leak, O2 Sensor, TB, CTS
Missfires under Boost Flashing CEL – Ignition Coils, Spark Plugs
Running Rich – Boost Leak, MAF, O2 Sensor, Coolant Temp Sensor
Running Lean – VAC Leak, MAF, O2 Sensor, Fuel Filter
Low Boost – Limp Mode, MBC, BOV, DV, Boost Leak, N75,
High Boost – MBC Setting, N75, Spark Plugs, Ignition Coils
Cold Start Problems – MAF, Spark Plugs, Fuel Pump Relay, CTS
Poor Gas Mileage – MAF, CTS, O2 Sensor, AIT Sensor
Cat Efficiency Below Threshold – Down pipe, CAT, Rear O2, RACE FUEL
No Start – Battery - ECU, Fuel Pump Relay, Ground
Start For 1 Second - Stall – Immobilizer
Overheating - Waterpump, Thermostat, Head Gasket
Oil in coolant - Oil Cooler, head Gasket, Water Wetter
Dies While Driving - Timing belt, Boost Leak, MISC
Shorts To ground CEL Fuel Pump Relay, Bad Grounds


Section 2 – Troubleshooting

Most of these procedures require a VAG com to scan the car for diagnostic codes. While you can fix things without a VAG you will most likely be replacing parts that really are not bad just to rule them out. A VAG COM is a must have for any 1.8T mechanic. Details here http://www.ross-tech.com/vag-com/cars/18T.html

AIT – Sensor – This is a small sensor located in the intake manifold just after the throttle body. It is responsible for monitoring the intake temperature. It can get coated with oil, and can affect gas mileage, and a loss of power. It is common to remove it and clean it with alcohol, or electronics cleaner.

Boost Leak – View Block 032 with VAG Com. If Fuel Trims are Negative more than 5% in the load range there is a very good chance that there is a leak after the turbo. Visual inspection of clamps, hoses for a loose connection is the best way to look for leaks. A common place for leaks is at the entrance to the pancake pipe located in the passenger side fender. Also the small line on the DV can rip.
Fuel Trim Details Here - http://www.ross-tech.com/vag-com/cars/fuel-trim.html

CAT – Aftermarket high Flow Cats often sacrifice emissions for power. It is not uncommon for aftermarket cats to give codes for “efficiency below threshold” right away. Some people have had success using O2 adapters to move the rear O2 sensor away from the exhaust gas and eliminating this code. O2 simulators do not work on the 1.8T. Sometimes cats can melt or clog up. Running hig exhaust gas temps for extended periods of time can cause this. Usually you will get the cat code, and see that the max boost and sustained boost levels drop off. After checking everything else on the list, remove the down pipe/cat and check to see that light shines through brightly. If there is very little light passing through it is clogged and requires replacement.

CTS – Coolant Temp Sensor – This part is prone to failure. 2002 and older vehicles had a bad coolant temp sensor from the factory that VW updated. It was a black sensor, and now the good one is referred to as a green top coolant temp sensor. Block 011 in the VAG COM can monitor coolant temp for erratic readings. This is a$13 part. Do not change while engine is hot.

Down-Pipe – See CAT

DV – Diverter Valve – When the throttle is closed on a turbo car, the turbo is spinning rapidly, and trying to push air into the engine. By closing the throttle the air has nowhere to go, and will cause a large pressure spike. The diverter valve is actuated by a vacuum line, and when the throttle closes creating vacuum behind it, the diverter valve will open and provide a path for the air. The air is returned back to the intake of the car after the MAF. When A DV fails it leaks air in this circular pattern causing boost problems.
2001 and older cars have a weak DV that is prone to failure. 2002 and newer cars have an improved design. It is durable, inexpensive (35$) and it responds very quickly. The part number for the good valve ends in 710 N. The DV is located at the back right side of the engine, it has 1 large hose, and 1 small line connected to it, and the other end is connected to your intake hose running to the airbox. To test if your DV has failed remove the DV, press the diaphragm up, put your thumb on the top nipple, and then release the diaphragm. There should be suction created on the top of the DV that prevents the diaphragm from returning. If there is no suction then the diaphragm is leaking and the valve should be replaced. IF the valve is good, check the VAC line leading up to the valve for any cut’s/ tears.

ECU – The ECU is responsible for nearly all functions on the car. If the ECU is suspected as a bad part, you need to use a scan tool such as a VAG com to attempt to communicate with the ECU. If you can’t communicate with the ECU, then the ECU needs replacement. Check all electrical connections. Check your Fuses for blown fuses. Whatever killed the ECU might kill the new one.
ECU removal procedure - http://www.goapr.com/VW/support/ecu_tt_golf_gti_jetta.pdf

Fuel pump Relay – The fuel pump relay is located under the driver’s side kick panel. Remove the lower panels to gain access to the relay box. When the fuel pump relay goes bad it will trigger many fault codes with electrical shorts to ground. The fuel pump relay is also used to turn on the injectors, and will show injector short to ground failures. If you open your door you hear the pump kick on, if the pump no longer kicks on, and you experience these codes repeatedly, replace the fuel pump relay.

Fuel Filter – The fuel filter on these cars is rated as a lifetime filter by VW. What the aftermarket has found is that high HP applications can run into fuel delivery problems with dirty fuel filters. 30K miles is a more realistic interval for replacement when pushing the system. The fuel filter is located under the car near the gas tank. It has small clip on hoses. To remove the hoses press in on the clip on the end of the hose and it will come off easily. You may need a small screwdriver for this, and be prepared to have fuel leaking out.

Head Gasket Head gaskets can be a cause of overheating, oil consumption or coolant in the oil. I have only heard of one case of a head gasket failure on a 1.8T and it was on a car running 30 lbs of boost and used head bolts. This is a repair better left to an experienced mechanic and is generally a last item to do after all other possibilites have been evaluated. overheating is usually the water pump, and coolant in the oil is usually the oil cooler failing internally.

Immobilizer – These cars are equipped with immobilizers to prevent theft. If you swap an ECU without matching up the ECU and the cluster, it will start briefly and then die repeatedly. There are 2 kinds of immobilizer. Immo II used on pre 2002, and Immo III used on 2002+. Immobilizer and ECU info can be found on the VAG COM Site.
http://www.ross-tech.com/vag-com/cars/immobilizer2.html
http://www.ross-tech.com/vag-com/cars/Immo3-ecu-swapping.html
If swapping an engine into a car without an immobilizer/cluster, you can get software for swaps from REVO, and Dahlback that remove the immobilizer.


Ignition Coils – These are famous parts for the 1.8T they are very prone to failure. VW has had a recall on these because they were failing rapidly on 2001+ cars. To check for bad coils the best way is with a VAG COM. Log Blocks 015, and 016. This will be a misfire counter. Drive the car or let it run, and look for misfires. If you have a bad coil you will see the counter increase on a cylinder. If you have one counting up then it’s probably a bad coil. Turn off engine and take that coil out and swap it with another coil. The cylinders read left to right 1,2,3,4 when looking at the engine from the front. Use the VAG again to see if the misfires have also swapped to another cylinder. If it moved, then you have a bad coil. Replace it. If they do not move, then you likely have a plug problem. On some cars the ignition coils have problems and they will pop up out of the cylinder head and lose contact with the plug. Plugs should be torqued to 22 ft-lbs when changed. If the coils still pop up, and they are torqued properly I have created a bracket kit to hold them down � – see sig.

Limp Mode – These cars are designed to protect themselves from engine damage. If the engine boosts too much, or the engine does not get enough fuel it will go into a limp mode where boost is limited to protect the engine. It limits boost by controlling a solenoid on the wastegate line (N75), by closing the electronic throttle or by opening the DV valve. If you are experiencing a limp mode the best thing to do is get the car scanned for codes and to see what is wrong. Look at fuel trims for signs of running lean, and to look for MAF problems, or O2 sensor problems. To look for potential boost problems log Block 115 and you can see the specified Vs actual boost. If you exceed the specified then there is a good chance that you will go into this limp mode. Stock specified is a max of 14 psi for a 2002+ car.

MAF – Mass air flow meter is used to measure the air going into the engine. It is located on the outlet of the airbox, and housed in a cylindrical tube. The ECU reads the MAF signal, and injects fuel in proportion to the airflow. There are a few different ways the MAF can fail. The MAF can get coated with oil, and will not read properly. This is common if it happens right after installing a CAI, or a K&N filter. It can be cleaned out with 99% isopropyl alcohol, or a quality electronics cleaner. Remove the sensor from the housing and clean the sensor element.
MAF sensors also go bad due to too much airflow. On a car with a larger turbo the airflow is so high that the MAF element will get burned out from the excess air flow. It is common to increase the size of the housing to prevent this (other modifications required).
To check for a BAD MAF the best way is with a VAG com. Block 002 show air mass from the sensor. At idle the air flow should be 2-4 grams/second. With a wide open throttle run to redline the reading should show up to 170 g/s on a chipped car. Look for jumpy readings in the MAF, which can indicate a problem. More details here http://www.ross-tech.com/vag-com/cars/fuel-trim.html if you suspect your MAF is bad, one way to test it is to unplug the MAF, often if the MAF is giving false readings and upsets the fueling. If you unplug it, the ECU will ignore the MAF and run off of baseline tables. Be careful, as a boost leak or a vacuum leak can be miss-diagnosed as a bad MAF, because they will throw off the readings on the MAF. (Air sneaks around the MAF).

MBC – Manual Boost Controller. Often people want more boost from their car, and use a MBC. While MBC’s can get you more boost they will cause a jerky part throttle driving, and can cause over boost, often put the car into a limp mode. The way a MBC works is by bleeding off air from the wastegate control line. A wastegate is a mechanical flapper valve in the turbocharger that opens to allow exhaust gas to sneak around the turbo. By bleeding off air from the line, the wastegate opens less, more exhaust goes through the turbo, and you get more boost.
Great details on MBC here - http://www.boostvalve.com/tech/1.8T-DBW.html
And general Turbo/Wastegate details here http://www.streetracersonline.com/articles/turbo/wastegate.php

N75 – The N75 is an electronic solenoid valve that the ECU uses to control boost. It is located in the intake hose near the back right side of the engine. It has 3 connections.
1. Connects to charge pipe = pressure source
2. Connects to wastegate actuator
3. Connects to intake hose – bleed line.
The ecu will pulse this valve at a high frequency to bleed air off from the wastegate line. It does this based on throttle position and engine load. If the valve, or any of the liens connected to it have leaks then there can be severe boost regulation problems. It’s function is similar to the MBC above. To get more boost people often swap in different N75 valves. These different valves simply have a different response characteristic, and will act different when given the same signal by the ecu. They can get more boost, less boost, or even a big boost spike by swapping N75’s.

O2 Sensor – Because of strict emissions these 1.8T’s are very sensitive to readings from the O2 sensors. MY 2001+ have a wideband front O2 sensor with high accuracy and a linear response. The car will adjust the fueling based on the readings from the sensor. If the sensor is over heated, exposed to lead (race gas), flooded with soot (too rich) or is just old, it can provide the car with false readings and the car will not provide the proper fueling. When the O2 sensors go bad and the ECU detects this the car will run on reserve fueling maps and will not be able to adjust for boost leaks, fuel pressure, MAF readings or any other parameter that affects fueling. To check for a bad sensor the first thing to do is run block 032 on the VAG com. If the sensors are bad, the readings will both be 0%, replace the Front O2 sensor. If the sensor is bad, it will also respond slowly, or reach a peak. Logging block 031 will show the lambda reading from the O2 sensor as well as the requested lambda from the ECU. To get air fuel ratio multiply lambda by 14.7. If the lgo shows the lambda jumping wildly when running through a gear, or perhaps it flat lines at an unreasonable level, then the O2 sensor should be replaced. It is a 50$ part. If the o2 sensors get shorted out or the wires get pulled, they will damage the ECU, be careful with the wiring on these sensors. 2000 and older cars do not have a wideband sensor, however they will still perform some adjustment of fueling based on the sensor.

Oil Cooler The Oild cooler on these cars uses a plate and plate heat exchanger. Oil on one side, coolant on the other side. Often the brazing on teh cooler can fail and oil and coolant mix together. This is often misdiagnosed as a bad head gasket. To test this remove the coolant hoses and apply air pressure to the oil cooler and watch for leaks. Oil cooler is located above the oil filter.

Spark plugs – With the weak coil packs that these cars have, and the high boost pressures that they run, the spark plugs are very important. Spark plugs on turbo cars need a nice tight gap 0.028” is recommended. Spark plugs may come “pre-gapped” however you should always check the gap, as the variation can be severe and will cause problems. Plugs are cheap, so the best way to troubleshoot is to replace them or pull them and check the gap. A good cheap replacement plug that is a bit cooler is an NGK-BKR7E copper plug. They need changing more frequently, however they are cheap.


Thermostat - Thermostats can be a source of overheating. Most common is the waterpump. Thermostats are relatively inexpensive, and can be change din a half hour. If your car overheats, or has a tendency to spike up in temp and then drop down to normal temp, it may be a thermostat.

Timing Belt If your driving along and your 60+K mile car runs great and all of a sudden dies, there is a good chance that your timing belt has broken, or stripped some teeth. This is a very costly repair and could have been prevented had the factory recommended a better service interval for the belt. Damage estimates are anywhere from 600 - 1800$ to repair this kind of failure. 60K miles is a good time to change the timing belt, some belts have lasted 90K, but it's not worth the risk. To test for this failure, pull off the timing belt cover and crank the engine by hand. If the cam gear doesn't turn you have a bad timing belt. Repair is best left to a good mechanic. - If your going full throttle and the car all of a sudden dies, check for a boost hose blown off -

TB – The throttle on these cars is drive by wire, it is an electronic throttle with a wire attached. Most common TB problem just requires adaptation, or cleaning out with carb cleaner. This procedure shows how to do a TBA. TBA can improve idle, and part throttle operation. http://www.ross-tech.com/vag-com/cars/throttlebody.html. To clean the TB remove it, and spray inside with carb cleaner. Wipe out the residue that gets built up in there. NEVER port a TB on a 1.8T it won’t idle properly.

Race Fuel – 1.8T engines love high octane fuel, however they can have cold startup problems, and if you run leaded race fuel you will ruin your Cat and your O2 sensors. Always run unleaded fuel in a 1.8T unless you are cat less, and you have extra o2 sensors.

VAC Leak – A VAC leak will cause un-metered air to enter the engine and it will run lean. If the air is not measured by the MAF then the fuel will not be injected. The O2 sensor will compensate for much of this, however it has limits. To check for a VAC leak, log block 032 and check the idle fuel trims. If it’s more than +2% you probably have a VAC leak somewhere. Check hoses and connections for loose clamps of cut hoses here are come common areas for VAC leaks.
Turbo inlet pipe not secured, DV line leaking, Crank case breather Y pipe split, Line on Fuel pressure regulator gets worn and leaks, intake manifold gasket can leak, and PCV line under intake manifold leaks. To find leaks some people spray ether, or starter spray around in the engine bay and listen for changes in idle speed. If you get a change from spraying in a certain area look for leaks there.


Waterpump - Nearly all overheating problems I have seen on these engines has been from the water pump. VW uses a plastic impellar that is splined/molded onto the shaft. These splines strip, or the pump cracks and the impellar slips on the shaft at high speeds. If your car is overheating best bet is to change the waterpump. You can do the T-stat first to see if your lucky but every time I have seen people try this it's the water pump anyways. This happens as early as 35K miles. While your in there doing the water pump, change the timing belt. Timing belts on these can go as early as 60K miles. There are several companies that make kits to do the timing belt and water pump. www.ecstuning.com is a good one.

Water wetter - Water wetter is an additive used to remove surface tension from water. It improves waters cooling ability in a cooling system as it prevents beading of the water, and raises the boiling point. Water wetter should not be used with G12 coolant. It is best for race cars running only water. If you add this to the coolant reservoir you get a nasty oily sludg in the reservoir. Flush coolant system and remove this.

 

Helpful links (*for most popular)

The TT section links thread - click here now


Hole in tranny (timing plug) and amount of tranny fluid

http://www.ttgallery.fotki.com/

Jeff Bipes How to page

After-run coolant pump 225 only

Alternator transplant complete!

Ball Joint Replacment How-To

Boost guage install *

Brake Light Switch

Coilpack Harness

Euro Dash install

Front Inner CV Boot *

Front swaybar bushing

Fuel Filter *

Fuse Panel Layout *

Hazard switch replacement *

How ESP, ABS work

License Plate Mount

Maintenance Intervals

O2 Sensor Mod **

OSIRdesign Smoked Corners

Rear brake pad replacement instructions

Reset Remote

Running Light / Park Light - Install, Part Numbers & Instructions

Thermostat

Timing Belt , Ribbed Belt , Tensioning Damper , Tensioning Roller , Water Pump and Coolant Service (1.8T Turbo 20V Valve) *

Wheel Spacer / Offset Calculator *****

Turn signal stalk

Techron

Clamping the Map Sensor aka "Diode Mod"

VAG Tool Locator

Octane Engine FAQ

Fuel Blending Calculator

TT BUYERS GUIDE - For those looking to buy a used mk1 TT **

Engine Oil Bible

Engine Diagnostic Code Table

HVAC Monitoring Channel Descriptions