So I've been chasing down a "ghost in the machine" and I now suspect it is possibly a MAF issue.

2001 A4 2.8L

I checked voltage and continuity at the MAF harness plug. Pins 1 + 2

I get 5v...which I suspect is proper as voltage ranges are from 5-12 normally. If it is supposed to be 12v, then this could be my problem and not the MAF

Anyway, plugging the harness back in and firing the engine, I get a constant reading of 5v with no fluctuation....even slightly revving the engine there is no change.

IF, 5v is proper to the MAF, is the non reading of any fluctuation at idle or revving an indication that the MAF is toast? Or does it sound like I have a low voltage to the MAF issue not allowing it to actually function?

I'd checked the Bentley manual and it states to check the MAF fuse, but could not find a chart where the fuse is.
ADDED:Found the wiring diagram in the Bentley manual on page Y650. Notation: D22 "Connector (over fuse 234), in wiring harness front, right". Is this an in line non replaceable fuse? (Haven't located it yet)

Car is in good shape and well maintained and no wire hacking, so the harnesses and grounds should be OK. Maybe a ground issue?

Any help would be appreciated!

 

If you disconnect the MAF and car runs fine, the MAF is bad. You see, the ECU can run the engine just fine with the O2 sensors and such. The MAF allows for more precise fuel air ratios but if the thing is giving the ECU erroneous data, the ECU won't really know any better and it will cause running issues. Once you determine that is IS the MAF sensor. Replace it but clear the codes from the ECU so it will forget those "bad memories"..

 

I disconnected the MAF and the idle fluctuates a bit for a few seconds and then smooths out. What does this determine?

BTW, is the MAF supposed to have a 12v supply?

 

I can't remember if it gets 12 volts or not. I'll look in the service manual I have to see. However, does the idle fluctuate every time you start the car with the MAF disconnected. Have you driven it with it disconnected. Do so and see how it runs.