cjromney

I have a 1994 90 Quattro CS with the 12v V6 (AAH).

It is running very rich all of the time. Once the engine warms up the check engine light comes on. I have the RossTech VAG software and am getting the following two codes:

00537 - Lambda (Oxygen Sensor) Regulation
08-10 - Control Limit Surpassed - Intermittent
00554 - Lambda (Oxygen Sensor) Regulation 2
08-10 - Control Limit Surpassed - Intermittent

I have already replaced the following:
Both O2 sensors with Bosch OEM.
Engine Coolant temp sensor.
MAF Sensor.
I had the fuel injectors refurbished and flow tested/calibrated.
I have tested the fuel pressure regulator. It functions correctly and does not leak.
I have checked the EVAP purge solenoid and it works and is not stuck open.
I have checked multiple times for vacuum leaks.
I really don't know what else there is to check. Am I missing something that has to do with emissions and air/fuel mixture?
I have taken my car to a few shops including an Audi/VW specialist and nobody can figure it out. They have all just said that all the sensors check out and work and that they don't know why the ECU keeps switching to full rich.
I have just about had enough with this car but still have hope that it is close to being fixed and that if a few of us here start brainstorming we can figure it out.

Thank you very much for any help or ideas.

CRAZY_RUSSIAN

can this be caused by failed cars?

BFives

Did you check for vacuum leaks?

twentysevenlitres

Assuming you mean the Cats, they don't have anything to do with fuel mixtures.
Blocked cats maybe?
O2 sensors are the primary means to adjust mixture on any fuel injected engine.

I would check your air filter and inlet tract for possible blockages. I'm doubting this makes any difference on EFI cars though.
I'd also start checking wire continuities - especially those on the 02 sensors
TPS maybe? Don't know how you test it though...

CRAZY_RUSSIAN

yes, sorry, cats

cjromney

Ok finally found it. The ground wire on the back of the intake manifold was loose. I cant believe it was so simple. Thanks for the input though.

twentysevenlitres

What was it the ground wire to?

cjromney

It comes out of the wire harness and bolts to the intake manifold near the throttle cable bracket. I may be wrong, but from what I understand it is a direct ground reference back to the ECU for the various sensors on the engine.