Not sure how the vdubs look under the hood, but if you have room, take the DV out and check the rubber diaphragm. If it is torn or crack you need a new one. If your idle is jumpy, listen for a leak somewhere...if the bad idle doesn't seem to be from a leak, my guess would be the crank position sensor.
My first car was a 90 passat, so I know about the wierd electrical problems, but a coolant temp sensor shouldn't have much to do with a bad idle and stalling, if that was the case i'd be looking at the temps on the cluster (idk if theyre controlled by the ecu or mechanical). if it stays in the cold, it would be a temp sensor or thermostat stuck open, overheating if it was stuck closed.
Check all your boost pipes, check the vacuum pump and brake booster for leaks. There's been a few times when I've sworn I checked all the lines for a leak and I always end up finding one when I go back and look.