I fixed the slight surging problem that I had on my 84 today. When I would stop at lights it would just surge a little every once in a while, like I didn't have my foot on the brake all the way. Anyway, what I did was bought a can of Gumout throttle body cleaner (other brands are fine) and started the engine. I took off the oil filler cap and the whistle started from the vacuum in it. I took the ENTIRE can and sprayed in the oil filler neck and mostly in the small hole that leads to the vacuum in the cap. It takes a while, because the car starts to rev down when more throttle cleaner is in there but once the bottle was empty, I tightened the cap back on and drove off. I had to drive slowly at first because it acts as if it wanted to stall with all the cleaner I just injected but after about 25 seconds, it was back to normal. Now when I stop at the lights I have not even the slightest amount of surge.

Hope this helps someone,


Along with all the items you mentioned, also be sure to check proper  operation of the throttle switch. It should have continuity at idle,  and again close to approaching full throttle. It is essentially a quick and easy bench test with an ohmmeter. The details are in the  shop manual. I can supply the specifics if needed.

Mine had continuity at idle, but not at WOT, thus a lean condition at  full throttle as a result. The TP switch anomaly is pretty common,  I've been told.
Mine was broken on the idle side, and only when hot. Engine would oscillate wildly and sometimes stall when trying to idle at a stop, usually just as I was hitting the throttle to go.

Replace it if there's any sign of problems..

88 S4