87.5 Coupe GT massive idle surge and trouble codes= ???

[J4KQ4me <J4KQ4me@aol.com>]

My friend's 87 coupe GT w/NG engine code has an intermittant crazy idle surge.
I'm talking from idle to 3000 or so RPM.  Today (It's an automatic) I was
driving it to try to diag the problem and the thing took off into the car in
front of me.
 Here's what I have done:
  1.Full tune up, checked for all vacuum leaks, and cleaned and lubed throttle
bod. and Idle stabilizer valve.- I have squeezed the hoses to the ISV to see
if it would idle down, and it will surge all the way to a stall.
  2. Found that code 2121 (Idle switch) comes up in the memory when it has the
probelm. I have checked the switch for continuity- good, for power at the
switch- good, and then to the FI ECU at pin 28. All checked out good. 
  3. Switched ECUs with another from my NG coupe. Same problem.
  4. When it's running okay, I've set all the engine specs to nominal.
 Now- I haven't pulled the center console out yet, so I am wondering if the
Ignition ECU could be sending that code, and not locking the timing down at
idle, causing it to fluctuate up and down. Any BTDT on this issue? Is this the
worst FI system Audi has ever used? My 87 coupe, my friend's 87 coupe and my
other friend's 87 5000s all with CIS-E III have idle and intermittant
performance problems.  Are there any updated that need to be performed on this
system?
 Thanks!
 Jon
 84 Coupe GT <New family member
 85 4KSQ < New engine recipient
 87.5 Coupe GT
 81 VW Rabbit conv.