Here's the quick background on the problem: Car was idling rough a few weeks ago. I changed the oil (just because it was scheduled) cleaned the throttle body and the IAC valve. Put the throttle body back on with a new gasket, throttle raced to ~3500 rpm

I just got back from pittsburgh this afternoon, and found my new throttle switch and other assorted parts waiting for me on the porch. I replaced the throttle switch, and the idle dropped down to about 2000 rpm. Here's the weird part: It stayed at 2000 for a few seconds. As long as the seat belt reminder light was on, to be exact. Then it dropped to almost stalling for a few seconds, and shot back up to 2000. Fluctuated like this for a while. Then it stayed at the high end (2000 - 2500 rpm). I had a spare IAC valve handy, so i put that in. no change. I screwed the idle adjustment screw in the whole way (the big black plastic one), and the idle lowered, but not enough.

So after all of this, is there something else that could be causing these symptoms? None of the gaskets/seals are leaing on the intake, and my only other guess is maybe there's a hole in the vacuum line to the ignition control unit, but i doubt that would cause such a massive idle response. A last ditch effort might be to replace the ECU (i have a spare), but i want everyone else's opinion before i go taking the inside of the car apart.

Thanks