Idle Hunting - '87 5kcstqw

[Swann, Benjamin R. (BSWANN)]

I'm sorting out issues with the new to me 5000 Turbo Quattro Avant.  This
problem cropped up while I was driving it back from Georgia to MD.  The car
began surging while I was driving it and slowed to speeds under 50 MPH.

I am trying to isolate culprit - engine is hunting for idle, revving to
about 1500RPM then dropping down to around 700 repeating about 1/sec.

I checked the throttle screw ( this had caused similar problem before with
my other '87 5kcstqw), the o-ring looked good.

I haven't found vacuem leaks - yet.

I disconnected the ISV connector - no change.  I forgot what is supposed to
happen.  I may resort to cleaning it, but dont think this is the problem.

I'll be checking the throttle switch next.

Looking for other ideas and clues.

TIA

Ben