Air Flow Potentiometer repositioned to fix idle problem

["Walt Dwarnick" <walthome@ptdprolog.net>]

I finally solved an intermittent idle problem that had be occurring for a
couple of years.  It's feels great to finally rid myself of this bug.  
Thanks to the tips I received from an earlier posting, I finally got to the
bottom of it. The problem was the air flow potentiometer.  

The air flow potentiometer is located on the passenger side of the air flow
meter body.  It has a three point connector that connects it to the ECU. 
As the air flow plate is pushed up by increased air flow the arm moves a
set of brushes across a resistance track.  
Point 1 is a constant 5 volt supply 
Point 3 is ground 
and Point 2 varies from 0 to 5 volts depending on the position of the air
flow plate.

When I took off the potentiometer, I found that the resistance track was
worn and that there was and an imperfection in the track.  This was causing
the ECU to loose the signal and drop to some sort of limp home mode where
the car still ran, but idled very low, about 400 rpm.   After stopping and
restarting the car everything would return to normal.  Although the check
engine light did NOT stay on, it did blink.   I checked the diagnostic got
a code 2232, which indicated the air flow sensor was not providing a
signal.

When I removed the potentiometer, I gently sanded the resistance tracks
with 2000 grit sand paper.  When I put it back on I repositioned the
potentiometer.  Although the specs call for about 0.14 with the car not
running, after repositioning it I could not achieve the same no run
setting.  By adjusting the set screw in the potentiometer, I was able to
achieve the 0.6 volt setting at idle and the 4.5 volt setting with a fully
lifted air flow plate.  The car runs great now.  I'm posting this to help
out other Audi Fans to save money.  A replacement of just the potentiometer
is not possible and the whole meter costs a lot, some $500.    


Walt Dwarnick

1989 Audi 90  5cyl FWD 164,000 mi