'87 4Kq idle blip

[Russ Maki <rinard@execpc.com>]

Hi folks,
I've gotten a lot out of the Quattro list over the past six months
without contributing anything. Sorry to say, but that isn't going to
change with this posting!
Unless, of course, a baffling riddle serves to enrich the list.
So here goes: My '87 4Kcs quattro has a weird, momentary (maybe 0.1
second) cycle in which the idle RPM rises from 8000 to 8100 or so. The
cycle occurs regularly every 1.5 seconds. Other than that, the idle is
steady and strong. Vacuum lines are tight. The car accelerates and runs
well, but I can feel the blip at low speeds when I take my foot off the
throttle (rolling through a parking lot, for instance).
The best Audi independent in Milwaukee has had the car for a week and
he's mystified. He says the ground in the idle stabilizer valve circuit
is interrupted, causing the blip, but he doesn't know why.
Any guesses? I thank you...My mechanic thanks you...
Russ Maki
'87 Audi 4000q
'87 BMW 325ic
'71 Mercedes-Benz 250