Odd idle...

[ORSOPERS]

I am hoping that someone can help me solve a strange (annoyance really)
problem my '88 80q is having.  Every once in a while the idle will 'bounce'
about once a second from 1000 rpm to 1200 rpm.  The circumstances where it
will do this are very specific, i.e. the motor is fully warmed up and then
shut off for 15-50 minutes and then restarted.  After restarting and driving
off, the first time you come to idle it will start bouncing.  If you turn
off the engine and restart it right back up the bouncing idle goes away and
wont come back unless you shut the engine off again.

Now I should say that it seems to be heat related, but I can't make it
happen.  It only happens about 1/3 of the time the conditions are met.

At one time I thought vacuum leak, but it goes away by stopping/starting the
engine.  I have checked the Idle Switch (new 10,000 miles ago) and it works
just fine, even when the motor is fully warm.  I have very recently replaced
both temp sensors (to match the new radiator and heater core - I have
pictures of the dash removed/heater core but they aren't for the faint of
heart) and the O2 sensor.

Any ideas?  I have to admit that this is a fairly minor annoyance but I
really do love this Audi and would like to see it run correctly.

Thanks so much for all the help and support,

Rand Soper
Portland, Or
'88 80q