I have a 88 n/a gxl. The idle jumps between 1400 and 1500 rpm. I'm pretty sure it's a vacuum leak, although I may have a tps problem too. I sprayed the whole engine bay with carb cleaner and the only place that seems to have a vacuum leak is beneath the UIM. I spray in there, sometimes it steadys the rpm, sometimes it doesn't.

I take off the UIM and all the hoses seem fine. No exposed nipples either. I was thinking it could be the UIM gasket, but that looks good. What could it be?

Using a digital meter, I set the UIM to 1k ohms. The the other test says that it should move steadily to 6k ohms i think. Mine gets to 6k ohms, but it's jumpy. (not sure about the 6k number. it was awhile ago) could that cause a jumpy idle?

 

start with the tps and read the idle faq.