Would upper leak cause this??

i dont know what the vacuum set up is on the track heat but i had a whistle back there and the hard tube from my fuel pressure reg was broke...is the pcv in the stock location back there? check that..just ideas..

What brand throttle body? Does it have a small pilot hole drilled through the blade?

"Setting" the TPS does nothing. The EEC references the voltage at startup and adjusts its range from there. So long as the TPS is good (read: within tolerance) then there's no advantage to having it set to a percieved sweet spot.

I'm guessing that your TB is a PP based on your "setting" the TPS voltage.

Where is the throttle stop set to? It sounds as if the stop may be too far out.

Also look at the throttle linkage itself where it conncts to the throttle body to ensure that it's not hanging up on anything.

Check all the ducting between the MAF and the throttle body to ensure it is air tight.

Potentially, yes. Short of having an AFR meter to see if you're running lean, you can try turning all the lights out in your garage and see if your headers are glowing (assuming you're running headers).

My point is that ANY inlet leak can cause the problem you describe but so can a host of other things. To me (granted I'm attempting to diagnose over the interwebz vs. looking at it) you description is making think that the throttle blade is being held just shy of completely closing. Air may be by-passing the IAC causing your idle to hang. It would also cause you to run lean at idle (i.e. glowing headers at idle with the lights out).

Try turning the throttle stop "in" a quarter turn at a time and driving for a bit to allow the EEC to readjust. It can be difficult to set the idle with the IAC disconnect method even if you ARE clearing EEC each time. That said... the EEC 'should' pick up minor changes after a time and come into it's own on settling for an idle (even with a slight inlet leak). Not so much if the throttle blade is no fully closing though. The TPS is helping to lie to the EEC about the position of the TB.

Worth a shot.

Good Luck!

sorry... another thought. Try manually closing the TB blade when it's idling high.