Hi. I have a 99 A6 2.8 Q tip. 170k+ miles. Recent timing belt service done.

Throwing these codes:


== 17546/P1138 - Fuel Trim: Bank 2 (Add): System too Lean ==
== 17544/P1136/004406 - Fuel Trim: Bank 1 (Add): System too Lean ==
=== 16806/P0422/001058 - Main Catalyst: Bank 1: Efficiency Below Threshold ===
== 16486/P0102/000258 - Mass Air Flow Sensor (MAF/G70): Signal too Low ==


For the last few months, it has run rough at low RPM after the car warms up. It starts and idles fine, and then after a few minutes (after going into closed loop I imagine) it has a loping idle. Occasionally will stall at a stoplight in D or in Park in the drive. It runs fine with normal power at speed on the road. I have just been putting up with it as the car only has to get me 1 mile down the road to work and back.

It has had all the codes except the MAF code until just the other day. Now it runs rough right off the bat, and I encountered the 16486. Did the MAF unplug test and idled much better. Figured, okay, this has been a slowly dying MAF all along. Get a new MAF installed, plug it in, and the problem came right back.

Do I need to give this 200 miles to fix itself? Or am I barking up the wrong tree. I initially thought maybe a vacuum leak as the engine runs better and better the high RPM you go. Then the MAF code came along.

Thanks for feedback!