So I did a search, and this is what I came up with...

First, the problem: So I get up to go to school, car starts fine, drives fine, nice easy cruise, not too much throttle...anyways, just as I am about to shut it off, the idle starts dropping to ~500rpm and back to 900~ repeatedly. It almost wants to stall out and then bounces right back. The car was in neutral with the clutch depressed and no electrical running except for an aftermarket deck.

Now the weird part...was changing the oil yesterday and I noticed that one of the vac lines was disconnected (hadn't seen a difference in driving with the vac line disconnected). I put the vac line back on, and nothing changed, so I assumed that everything was alright.

Now the fix: When I get home from school today, going to look at TPS, Idle Adjustment screw on throttle body, plugs, wires, and all vac lines again. Is there anything else that I should be checking? In some other threads it has also been mentionned that water temp sensors and O2 sensors can also cause this problem...is that correct???

BTW my car is an '87 GXL with streetport and custom exhaust.

Thanks for the help,
Brad