I just purchased a 1999 A6Q from a local Colorado Dealer, and at 97,640-miles have pulled multiple DTC codes as follows immediately after leaving lot:

17535 long term trim system too rich bank-1

17537 long term trim system too rich bank-2

17549 load calculation cross check implausible value P1141

At 96,500 the local dealer noted possible Throttle Body issues, and the smaller dealer that sold me the car claimed they had a shop replace the Mass Air Sensor. Idle seems erratic bouncing between 500-800 rpm at idle, and extremely rough engine when driving after warm start.

Any suggestions for an underlying problem/remedy would be much appreciated

 

With the first two fault codes you listed you either have a bad MAF sensor, O2 sensor(s) or at least one faulty fuel injector. If you have access to VAGCOM/RossTech you can monitor the values with your pc while the engine is running and diagnose the issues from there with much more precision.

The last fault code you listed would most likely be caused by a faulty MAF Sensor, MAP sensor or a fairly large vaccum leak. If were you, unless the indie shop provides paperwork proving the MAF sensor was replaced, I would tend to lean towards the diagnosis provided by the Audi dealer. And if you indeed have a serious enough vaccum leak you should be able to hear a hissing or a sucking noise when the car is running.

Anyway good luck with it. Hope you get your car running properly soon.