When the engine is cold, the car will not give me a idle speed high enough to keep it running.
As it heats up (about 1min of keeping the revs at 1500-2000), i let go of the pedal. Revs fall down to ~100, it coughs a bit, and it jumps back up to 5-600.

As it heats up, it will gradually get up to 900rpm, where it sticks. Engine runs a bit bad as it heats up, but is fine-ish when it has gotten up to 90*c (usual running temp)

Lately fuel economy has become worse, and it has an avg fuel consumption of 10l / 100km, it is a small 1600cc block.

 

This is what VAGCOM gives me:

VAG-COM Version: Release 409.1-S


Chassis Type: 8D - Audi A4 B5
Scan: 01,02,03,08,15,17,25,35,45,55,56

-------------------------------------------------------------------------------
Address 01: Engine
Controller: 8D0 907 558 A
Component: 1,6L R4/2V MOTR HS D05
Coding: 04001
Shop #: WSC 00000
1 Fault Found:
00670 - Throttle Position Sensor (G127)
27-00 - Implausible Signal
Readiness: N/A

-------------------------------------------------------------------------------
Address 03: ABS Brakes
Controller: 8E0 614 111 AB
Component: ABS 5.3 FRONT D00
Coding: 0273004281
Shop #: BB 24548
No fault code found.

-------------------------------------------------------------------------------
Skipping Address 15-Airbags

-------------------------------------------------------------------------------
Address 17: Instruments
Controller: 8D0 919 034 B
Component: B5-KOMBIINSTRUMENT D10
Coding: 00142
Shop #: WSC 00150
No fault code found.

-------------------------------------------------------------------------------
Address 25: Immobilizer
Controller: 4A0 953 234 F
Component: IMMO AUZ9Z0V5221729 D77
Coding: 00000
Shop #: WSC 00012
No fault code found.

End --------------------------------------------------------------------------------------------------

 

Bumping this..! Noone knows!

Problem has escalated to having difficulties starting, and rpm meter shows revving from 2700 to 0, goes up and down for a minute.
Problem with knock sensor, but only when engine is cold? Where is the logic?

 

Have you tried using VagCom to do a throttle body alignment? If you have a drive-by-wire (DBW) car, you can initiate a TBA using VagCom. Or you can disconnect the battery for a few minutes, then reconnect it, and turn the key to full electrical power (right before the crank position), and you should hear the TB humming underhood as it aligns. Try it out - it can't hurt anything and may help you out. It's a good first step.

 

have you recently swapped ECU's or installed a new or used one?

you have a code for throttle position sensor, if you do a TB alignment and that doesnt help you will need to replace your throttle body. that is most likely what is causing it.

 

ImTheDevil, I have the pre-facelift B5s, I think DBW came after 99.
It's a 97 mod. I guess it's mechanical, though the throttle opening (don't know English word for it!) can open by itself without me toucing the pedal (some kind of motor? Don't quite know how it works!).

ghost6306
I have not, but I have disconnected my battery alot when working on the car.
Replacing my throttle body sounds expensive by the way! Can throttle body alignments be done to cars without DBW?

 

yes they can, you can do it in vag-com. there is a walk thru on how on the vag-com website: ross-tech.com

after you remove the battery you always have to do a throttle alignment. that is probably the reason your car is doing this.

 

Oh, thought this only was required on dbw cars. That might be the culprit.
I only have a cheap vagcom cable with v409.. I need a newer one, right?

 

Went outside to test a bit now....

I started vagcom, went to engine, measure blocks and went for Group 098, as specified on the rosstech wiki. Ignition on, engine off.

This is my first result:


Trying to reset to default settings:



The voltages I got was 4.1v and a fluctating voltage at around 3.1v. Only slight fluctation, though. It displayed ERROR in the right info frame, instead of ADP OK which we got later (ADP is my engine code).
When I plug out the big-ish plug at the throttle body, both voltage-sensoring units give me a flat 5.1v.
Can still give throttle to the engine, but no result on the vagcom output.


Revs are jumping up and down while the plug is out, at 1500rpm +/- 300

After we plugged the plug back in, we were actually able to reset the throttle body successfully.



By the time we had come to this, the engine was warm and we didn't really know if the problem was persistent or not.. However, the idle was still fluctating slightly around 900, as it always has. Fault code did not come when we tested it when it was warm.
Will post diagnostics fault codes when it's cooled down, in a couple of hours!

 

Switched the engine on, it acted as normal as it gets. Revved up to 1300, then fell gradually down to a steady-ish 900rpm idle. The throttle realigning worked, great.

Now my next problem is that the idle is well.. ****. It doesn't stay steady, and it revs up and down whenever i do a full stop, and put it in gear again.
Ie. i stop to park, put it in reverse, and it just gives throttle by itself, and i just feel the pedal moving away from my foot by itself.. Bouncing up and down a bit before it settles. Very strange, and not very cool.. Anyone have any idea what I'm talking about?