Not sure how to correlate the 2 symptoms, but you may as well tackle the idle issue first (testing under idle conditions is easier than boost).

If you checked, swapped, putzed with everything, I guess that means you verified the TPS switch function by measuring it at the ECU end of the wire, and cleaned the IAC valve?

When I cleaned my IAC, I also checked its function by blowing air through it while changing applied voltage. Experiment by very briefly applying voltage to its pins. On the 3-pin type, connect +12 volts to the centre pin, and alternate ground between the two outside pins. On the 2-pin type, voltage only gets applied during idle. Try the voltage both ways, to see which is right (as long as it's just brief "bursts" of voltage, you can't hurt it). Either unit should pass air in one voltage scenario, but not in the other.

If you've done the above, and still get no idle change when unplugging the IAC, there are two checks left (either check can be done first):

IAC AIR FLOW

Do a positve verification of air flow through the IAC. Disconnect the inlet side IAC hose from the main intake accordian hose. (You may need to block off the opening on the side of the accordian hose). Now verify that the disconnected hose pulls in air during idle (or blow into it if that's what it takes to prove it's passing air). Then push the throttle slightly off its endstop, and see if the hose still pulls air. It shouldn't at this point (at least not very much).


If it passes the above test, the IAC is working fine. If not, it could be either the driving voltage, or the valve itself

IAC DRIVE VOLTAGE

Unplug the IAC, and measure voltage across the cable connector pins. I believe it's a pulsed voltage, so you're best using an analog meter, which averages out the variations. (For the 3-pin type, the centre pin is +12 volts - take measurements between the center and both outside pins). Do the measurements while at idle, and repeat for when the throttle is slightly off idle. For either pin type, there should be an obvious difference between idle and off-idle.

You should know by this point if you have an IAC problem, and what it is.
--
David Armstrong - '86 240(350k km?), '93 940T(270k km), '89 240(parts source for others) near Toronto