Perhaps time to get back to basics. If the TPS, IAC and ECT more or less check out electrically then I think your talking too much air. There are a few possibilities. I'll dump all my thoughts here in one go.

If the engine is running rough then it's likely too much unmetered air, i.e. a vacuum leak. For vacuum leaks, check for disconnected/split hoses going to the throttle body -check both ends, check the hose going to the evaporative control (charcoal) canister (below and behind the left headlamp assembly), check for splits in the accordion section of the main air intake tube. Based on what you've said so far I don't think you've got a simple vacuum leak.

So let's assume there's too much metered air, i.e. too much air getting past the throttle plate. That either means the IAC is allowing too much bypass air or the throttle plate itself is too open.

To check out the case where the IAC is allowing too much bypass air, try the following. FYI With your LH 2.4 system the IAC is a two wire valve normally kept closed by a spring while the older type (found on 240's with LH 2.2) is a three wire valve and the piston floats free. So for your system, when the idle is too high and with the engine fully warmed, just unplug the IAC connector to fully close it. If the idle drops then the IAC is being held too far open by the ECU and the problem is likely elsewhere, especially a sensor (like the ECT). If the idle doesn't drop then either the IAC is sticking open or the ECU already has it fully closed and the problem is elsewhere (like the throttle plate).

A quick check for a sticking IAC is to tap it rapidly with the end of a stick and see if the idle drops. As you've done, using the OBD test to cycle the IAC wide open is useful and if repeated many times often helps to refresh the full range of valve movement.

In your case, I'm very suspicious that as your engine warms up, the IAC is quickly being put in the fully closed position by the ECU, but there is simply too much air still getting past the throttle plate, i.e. the plate isn't properly closing. Once properly set, there should be no need to touch any of the throttle body adjustments (from the TPS right up to the throttle cable), but if there is any chance they have been touched then a full readjustment is in order (don't feel too bad if it's you, I've been there myself trying to get my 16 valve to idle nice and smooth).

Although unlikely in your case, if the throttle plate is simply sticking, try to manually close it and see if the idle drops. The throat could be dirty or the throttle shaft could be set too far into the TPS and binding.

Now in your case, as you've already checked the common idle culprits, I'd want to make sure the throttle body is indeed properly adjusted before going further. I'll start by noting that the adjustment procedure in the FAQ for the throttle position switch is not as precise as it could be plus there are different procedures for Bosch and VDO switches. For a proper throttle body adjustment you should proceed as follows (I've posted this before, but can't find it):

1) Open the lower end cap of the throttle linkage rod, pop off the end cap and remove the throttle body. Thoroughly clean the throat, plate and vacuum orifices. You can remove the brass vacuum fittings to clear them. Blow out the small orifices through to the throat (a needle and small drill bit can be carefully used to ream the orifices if needed). While you're at it, make sure the small hose from the throttle body to the flame trap is clear -not uncommon to be plugged for cars driven very short distances.
2) On the throttle body, back off the idle stop screw. Loosen the TPS switch. If you have any doubts about the TPS switch then test with an ohmmeter connected between the centre and outer pin (one outer pin is for idle closed the other pin is for WOT full open -not used by LH 2.4).
3) Make sure the throttle plate is centered and can close properly without binding -look through the throttle body at a light source and ensure an even ring of space around the edge when closed.
4) Hold the plate closed. Advance the idle stop screw until it just touches the stop and the plate is about to start opening. Advance 1/4 turn more then secure with the lock nut.
5) Adjust the TPS switch. As you know, it should click just as you move the throttle away from its stop (and click again on the return). For proper adjustment start with the switch rotated clockwise away from the stop position. For a Bosch switch, hold the throttle plate closed, turn the switch counter-clockwise until it clicks then continue to end of travel and lock in place. For a VDO switch, insert a .010" feeler gauge at the idle stop screw (if you don't have a suitable feeler gauge substitute two strips of medium heavy bond 24 lb. computer paper), turn the switch slowly counter-clockwise until the click is heard then lock in place.
6) Re-mount the throttle body. Use a new gasket unless the old one is in perfect shape. Connect and adjust the linkage rod as follows. These aren't critical adjustments, but they are the official specs. For a B230FT (or B230F on a 740), insert a .10" feeler gauge at the throttle *spindle* stop tab (not the idle stop screw). Adjust the linkage rod so that the throttle begins to open and the TPS click is heard then adjust it back to the point where the closing click is just heard and secure the rod adjusting nuts. For a B230F on a 240 use a .08" feeler. For a B234F use a .13" feeler (.06" for the early '89 production B234F's w/auto trans).
7) Re-adjust the accelerator (gas pedal) cable as needed for a little slack making sure the cable is properly seated in the spindle.
8) For an automatic, you should then re-adjust the downshift cable (next to the throttle cable) -see the FAQ.
9) Re-install all vacuum lines. Replace any that are split or loose on their fittings. Make sure you haven't pulled the other end of the lines off their fittings, especially the ones on the charcoal canister (big black plastic canister up front, typically behind and below the left front headlamp assembly). Don't forget to replace the TPS connector -easily forgotten.
10) For an LH 2.2 system, check/reset the base idle using the thumbscrew while grounding the idle control valve signal from the open test connector on the fender -see the FAQ.

Now the throttle body and TPS should be out of the equation. I really hope somewhere in the above you'll find a fresh lead to your problem.
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Dave -940's, prev 740/240/140/120 You'd think I'd have learned by now