[1988 90Q MT] Fault Codes

[James Wagner]

Once I replaced the bulb and holder for the "Check Engine" light (that the
previous owner REMOVED AND THREW AWAY), I found a couple of codes would come
up when I checked per the Bentley manual.  I unfortunately didn't realize
this until I got sick of it misbehaving at idle and having truly horrible
inconsistent full-throttle performance.

2142 (Knock Sensor) - I checked this with an oscilloscope, and it speaks
when tapped.  However, insulation is cracked from the wiring and there might
be an intermittent open, so I'll be replacing this.

2132 (California Only - no data transferred betw. FI and IGN units) - I
don't understand why this code comes up twice in succession, or why it's
happening on my non-california car.  I'm assuming it's non-california car,
because it has to EGR... is there a better way?  Is Bentley just wrong about
this being a Cali-only code?

4431 (Idle Stabilizer) - "problem in wiring" according to Bentley, although
you can hear it clacking away when doing the output checks.  The car idles
too high(~1200 revs) and occasionally dithers between 1000 and 1400 rapidly
when warm.  I've checked the valve, and when it's at rest you can blow air
through it - the "window" is partially open at rest. I'm thinking that the
soft brass adjustable "stop" it has been hitting for the past 13 years has
allowed the little rotary valve to close too far, which actually results in
it being open.

2123 (Full Throttle Switch) - My Fluke says it's fine.  The output checks
don't behave like the Bentley says; the 4341, 4343 and 4431 tests run
whether or not you're pressing the WOT switch.  The 4443 test is the only
one that behaves like Bentley says.

I'm really, really frustrated with this car.  It's nearing 200,000 miles and
something new seems to break every day. I could recite a litany of things I
need to take care of, and things I've already done.  I fell in love with it
last Minnesota winter, but I'm getting ready to push it off a cliff right
now.   I'm not a rich man...

Thanks in advance,
Jim

1988 Audi 90 Quattro, 198,000 miles (VIN W.AU.H.C.0.89.4.J.A.235703)