I have a Mk1 VW Golf/Rabbit with K-Jet mechanical injection. Occasionally when I pull up at stop lights the engine idle will rhythmically dip and climb (between 600 and 1200 rpm). This probably happens 1/6 times I stop and it doesnt seem to matter what temperature the engines at.
The car feels and drives fine otherwise.
I would think this might have something to do with a vacuum leak but if that were true I would assume the problem would be consistent and not happening randomly. That being said, I am pretty sure the brake booster is knackered so their might be some issue there.
I'm not sure about the idle control valve either as the car has no air-conditioning so nothing drawing large amounts of power at idle (is this what the IAC valve does?).
Would anyone know what could be causing this and what I should be looking for?