cooltsi

My 2002 A6 with the 3.0 has 191K now and has developed a new problem. Once the car is warmed up and now it's getting warmer outside if I'm sitting at a stop light the RPM's will drop about 200 and the car will "shutter". It doesn't seem to do it when cold or when it's colder outside. As an experiment I have been putting it in neutral at stoplights and watching the RPM's, it still occurs but I can't feel or hear it. I did notice once that the volt meter dropped at the same time as well. My only know issue to this point is an occasional heater on the Bank 2 primary O2 sensor, which will occur twice until the car is warm. I haven't been able to correlate the O2 sensor heater to the observation. Any thoughts?

johnkk

The clue may be that the problem only occurs when the engine goes out of open loop at start and into closed loop operation when warmed up. Could be the MAF sensor is starting to go or the O2 sensor is causing it. To check the MAF, unplug it when the problem is active and see if the problem goes away. That would point to the MAF. Cleaning with spray, might help(never has for me). When my MAF went, the hesitation was more violent, so your O2 sensor might be causing the issue. Try cleaning the O2 plug connection at the firewall. Usually doesn't help there either, but you might be lucky.

Harleyguy

Scan for codes.

cooltsi

P0050 - Powertrain HO2S heater Control Circuit (Bank 2 Sensor 1)

clancy

How many miles since the front O2 sensors have been replaced?

cooltsi

Bank 2 pre and post O2 sensor were replaced last fall (September?) for the same P0050 error and I've put about 3K on the car since then. Cleared the error for a few months and it started occuring again about 2 months ago. I don't have any records for Bank 1. I'm seeing good movement in A/F ratio on Bank 1 for both pre and post, so I haven't been concerned. Bank2 has always been more lethargic.

I'm not seeing how the O2 sensor could cause the momentary bucking and RPM reduction? Car is actually running quite well most of the time. It did it last night as the car was relatively cold (needle just a smidge over 150 on the guage) while backing out to head home from work and behaved itself the rest of the way home.

Harleyguy

Entirely possible the replacement parts were/ are defective. What was the source of the parts? Reliable manufacturer or cheap knock-offs? Otherwise start checking the wiring to be sure all is intact and secure. Don't understand how this could cause your symptoms? The O2 sensors tell the ECM how well the fuel is burning (too rich, too lean) and tells the fuel system how to react. If it tells the system to change the fuel delivery based on the wrong reading the engine will buck or misfire/ hesitate. i.e.> if it says the mix is too lean and suddenly applies increased fuel the engine will stumble.

cooltsi

Wouldn't I get a misfire code or start seeing indications in the post cat sensor efficiency? It baffles me that I'm not seeing an indications as audi seems to be very sensitive to running conditions and setting the check engine. Haven' seen misfired since changing to the r8 coils.

Harleyguy

Look at your own previous post. It is telling you that there is a problem with O2 sensors on the bank in question.