2002 A6 Quattro 3.0

Just had the plugs replaced at 92K. Mechanic also replaced a vacuum hose that runs from the back of the PSP, down the length of the engine and disappears at the back (I have no idea what it was)

The ESP was always on (I had no ABS), but now that light is out, so maybe I have ABS again. Can't tell.

The CEL is on full time again....... this time it isn't throwing a P0421 code but rather a P0171 and a P0174. Both say mixture too lean etc. What's amazing is that when I do a code reset , the car literally just barely holds an idle and it's ready to die ..it will chug for a minute and then the CEL comes on and it starts to idle normally. I guess the O2's are kicking into self regulate mode on trying to get the right fuel/air mixture. Which also tells me, the O2's are saying don't do a code reset again, or else.

This is no way to run a railroad, as it will never pass emissions with the CEL light on.

Is it time for new 02 sensors ? Ideas ?

Thanks ...............

 

First clean the MAF sensor. If the codes come back, than you have a vacuum leak somewhere.

Also, ooooh, don't you worry, if you fix the P0171 and P0174, you will most likely get the catalytic converter code back.

 

If the engine is running to lean you may have a vacuum leak. The unmetered air is entering the engine and messing up the mixture, more air with the same amount of gas mean a lean condition.

 

All,

Cleaned the MAF, and the problem went away for a bit.

Here's the latest. I just had all DI Coils replaced under the recall by the dealership. While being replaced the mechanic found a vacuum leak directly under the Audi cover plate (OOOOO) at the rear of the engine, he ran a new piece of tubing and the problem seems OK.

HXGASER was dead on however, as the CEL came on a day later and damned if it wasn't a P0421 code again. You must be clairvoyant.

Need to get the word out that most Audi dealerships have the coils in stock under the recall and are setting appointments now for customers to come in. I don't have a link, however most customers should have gotten a notice in the mail over the past few weeks.

Thanks ........ DB