1988 Audi 90 5cyl -warm idle & other problems

[Chris Roden]

This is a multi-part message in MIME format.
--
[ Picked text/plain from multipart/alternative ]
Help - warm idle and other problems,
I have a 1988 Audi 90, 5 cyl, 5 sp, non turbo, with several problems. (this=
 vehicle has separate ignition and fuel injection computers)

The main problem is that once the car is warmed up, the idle is very poor, =
usually very low around 300-400 rpm. If I insert the fuse into the top of t=
he relay, to dump the codes while the car is running, the idle will jump up=
 to where its supposed to be (700-900) and stay there until I remove the fu=
se and then push on the throttle.  After that the idle will return to its c=
rappy state. Around 400 rpm.  (idle switch checks ok, and is closed when in=
 idle position)

I have 2 other issues, the first is occational stuttering while acceleratin=
g=2E  This is not very pronounced, and does not occur all the time, and is =
most likely to occur during very hard acceleration.  This is also an issue =
that the car has had for a long time - 5years, in which time I have replace=
, a fuel pump, an O2 sensor, a fuel filter, all for regular maintenance. La=
tely it has gotten worse, and more pronounced.

The other issue is varying idle during warmup. During the warm-up period th=
e idle will vary between 2000 and 1000.  It will do this fairly rhythmicall=
y=2E I put a timing light on it and noticed, that during the faster idle, t=
he timing was 12 deg. BTDC, and when the engine slowed to 1000 rpm, the tim=
ing dropped to 6 deg. BTDC.  The timing seemed to continue varying with the=
 idle speed for 2-3 minutes while the engine warmed up, after which time th=
e idle usually stabilize, and then usually deteriates to the 300-400 rpm. T=
his issue is newer, and seemed to show up, when I started getting the 2232 =
error code - airflow sensor pot.

I have not been able to clear the error codes, with any of the prescribed m=
ethods, except removing battery power to the computer.  I have a spare igni=
tion computer, and it does not appear to make any difference, so I assume i=
t is OK.
The one code I always get is 2232 - airflow sensor pot.
I checked the voltage between terminal 3 and 1 while the unit was plugged i=
n and the ignition was on.  It was 4.85volts.  This value did not change as=
 I lifted the airflow sensor.
I have gotten some other error codes, but consider them suspect because of =
all unplugging and testing I have done.  I did recently get the code about =
the computers not talking to each other.
Here are some of the other items I have checked and their measurements.
Full throttle and idle switches both - 6 Ohms closed - infinite Ohms open.
O2 sensor voltage out once warmed up - 0.62 volts fairly constant (+- 0.02 =
volts).
Differential pressure regulator current is 100mA with the ignition on, and =
before starting. After starting the current drops to 0.1 - 0.3 mA staying f=
airly constant.
Dual temperature sensors 1690 Ohms cool (70deg), 380 Ohms warm.
Also the O2 sensor is fairly new less that 10,000 miles on it.

I have also checked some of the standards, Grounds at intake manifold are i=
n good shape. All fuses appear to be in their correct places, (2 engine fus=
es, next to spare slots, actually have a red cover over them with the word =
"Motor" on it).  No apperent vacuum leaks, but are there any areas that I s=
hould specifically check?

Any help would be extremely welcome. I'm considering getting a used FI comp=
uter from an auto recycler, but am wondering how robust these are, and if a=
 used one is also likely to have issues.
--