Just had a check engine lamp come on, again. It is very intermittent and car runs normal. Had local garage, non audi check codes and received P1128 and P1130. He felt this was the oxygen sensor? Any thoughts from people who know? Also, is this something that needs to get done ASAP and if so where is a good online audit parts site.

Any help is GREATLY APPRECIATED.

Sorry,
This is a 2000 A6 Quattro w/4.2. The check engine Lamp willcome on for a day or 2, go out for 3 to 5 days then come back on again.[>:]

Its probably a vacuum leak or a mass airflow sensor. Those faults are for both banks being too lean. Basically your getting too much air or not enought fuel. I doubt both oxygen sensors would go bad at the same time. Also check your intake manifold bolts. Sometimes they come loose.

Any Idea where the Mass Air Flow Sensor is located?

It is going to be locatedright after the airfilter before the intake manifold

My 2001 2.7T has a similar issue. The engine light would come on for few days, then it would go out for few days. I had it checked by a local Audi dealer. They said that it was related to the catalytic converter going bad.

they try to pull that on me to make $ but I did not believe it and took it to an indy shop.
it was just a sensor on code p1130
I would suggest a sensor or leak.
However, if it is the cat conmverter, it is convered under emmission warranty which is like 7 or 8 years I think.

"The MAF sensor could be bad. But the P1128 is triggered when the fuel mixture is so lean the O2 sensors are constantly in the rich position. I would look at the O2 sensors first. Then check the fuel injectors, fuel pump pressure and volume. Replacing the fuel filter is a good idea also. Vacuum leaks could cause the lean condition as well. I would make sure there are no vacuum leaks and that the oil cap and dipstick are firmly seated."
"Sorry it took so long. P1128 proprietary code is common on VWs and Audis. It sets when the long term fuel trim maxes out positive. Usually it's the result of a bad MAF sensor. VW and Audi have extended their warranty to 7 years I think to cover faulty MAFs. Before changing that, check that there are no unmetered air leaks, or broken vacuum hoses or anything that might create a vacuum leak and set the P1128. Start there, with that code first."

I'd like to thank all those who responded to my call for help. It is greatly appreciated and I have much to look at. One last question, Is this something I have to find/fix ASAP? It appears there could be O2 and/or AMS. Car Just last week past emission test in Maryland.

Generally its not a good idea to drive a turbocharged car that is running lean due to the increased chance of detonation and engine damage, however your car is equiped with an exhaust gas temp sensor which in theroy should reduce boost pressures when excessive temperatures are detected to prevent engine damage. In any case, these cars usually only run lean at idle when there is a problem and are fine durning other operating conditions. The ecm also compensates for the lean condition by adding more fuel to keep the engine running properly. So to sum all that up in laymans terms(sorry i get carried away with the technical stuff sometimes), you shouldnt do any damage to the engine by continuing to drive it like that.

This is a non turbo engine, 4.2 v8

if the check engione starts blinking, stop driving!

This is a non turbo engine, 4.2 v8
Sorry got a couple posts mixed up. Running lean on a naturally aspirated motor can be bad too, but the potential for disaster is far less than on a boosted engine. In any case as i mentioned above, the ecm is adding fuel to componsate so youll be fine to drive like that. Flashing check engine light indicates damge to catalytic converters is occuring, not engine damage. You should never drive on a flashing check engine light thou.