I keep getting returning P1128 and P1136 CEL. I cannot figure out what or why and I am looking for additional suggestions as to what may be the cause.

First off I have a 1998 2.8L, 30-v, Quattro 5-speed. I already replaced both left and right side exhaust pipes/catalytic converters (Audi OEM), replaced all 4 O2 sensors (Audi OEM), checked every single vacuum hose on the vehicle (none cracked) and I checked every other connection for the SAI system.

I also had the Audi Indy put in new plugs (OEM) and a new Coolant Temp Sensor while they replaced the valve cover gaskets and valley seals.

With 126,000 miles the car runs perfectly. Starts up and goes to about 1,100 rpm then drops to about 800 once warm. No issues with power. Only odd thing is once in a while when I drive somewhere, turn off for a couple minutes then try to start - it won’t start. Turns over but won’t start. If I wait about 10 minutes it fires up like nothing ever happened. Sometimes I push the pedal to the floor and override the fuel injection and it fires up. Sometimes not. Make me think it floods somehow and needs to drain before it will start?

When searching the possible issues that one or both CEL could cause, I get a myriad of possible things to look at. A lot of it I have addressed above. What is the next thing to look for?

Here is the search list of items from p1128 and P1136 searches and what I have already done:
•TB adaptation – performed using battery kill and key switch method. Seems to work but not sure.
• O2 sensor – all 4 replaced with Audi OEM
• Bad Cats – both are brand spankin’ new
• Vacuum leak – none found
• Check Valves – Only one blue/black one visible up near the hose bundle. Looks OK.

Other things that I have found may be suspect not yet tackled:
• MAF – Where is this on a 98’ 2.8L, 30v?
• N80/N75 valve – what and where is this?

Another thing I noticed in my engine overview. I have a hose that connects both valve covers to each other. Basically each valve cover has a nipple that faces the center of the engine and one hose connected to both. Each end has a slip-on factory fitting that looks to be made for the VC nipple – but one end is broke. Just the clip end that goes over the nipple. Could this be the leak? I can’t find anything close to this fitting online and may be a dealer part?

Last piece of the puzzle is before I replaced the cats and O2, I was getting the usual O2 CEL and Bad Cat CEL (forget the numbers). Those are now gone. However my gas mileage before the cat/O2 replacements was about 22 mpg. After the Cat and O2 replacement I am getting 16mpg. That leads me to think vacuum leak and causing the engine to over compensate with fuel and causing the bad mpg.

Any other quick hits to check? Please any input or advice is extremely helpfull. Otherwise it goes to the Audi Indy again to diagnose. I am just sick of the CEL on all the time. But more importantly I don't want to destroy the new cats. I paid a $hitload to have the done thinking it would solve the CEL (which it sort of did, the cat CEL anyway...)

 

Nobody knows nuthing, huh?

 

when my MAF on my 2001 a4 1.8t went out, it would throw lean codes. You might want to test it.

 

Turns out that the place that installed the cats and O2 sensors flip-flopped the pre/post positions and had them plugged into the wrong spots. Also a vac line had a tiny slice in it.

The occasional non-start is due to an engine speed sensor starting to go. Apparently when these start to go, when they get heated up from the engine temps, they need to cool down in order for the car to start again. It explains the 10 minute wait time needed from a non-start. Another quick and easy fix.

 

After 3 days of no CEL it popped up yesterday. Now a P0422 which looks to be a bad cat.

Now I get to go back to the pipe/cat/O2 sensor install place and force them to replace the cats/pipes. Since they %^&* up the sensors, the engine probably dumped enough raw fuel to destroy brand new cats. I am so pissed off right now. I can't win.

I see a small claims court case in my near future.