I can think of 3 things you can try:

1. Measure the resistance of that temp-sensor when cold. Depending on outside temperate - cold temperatures range is between approx 2000 - 6000 ohms. You need to check that it is not measuring <100 ohms or thereabouts, because that would indicate a hot engine to the ECU. (more info here). When measuring resistance, verify this at the ECU (or CIS control) end as well

2. Rig up this test LED setup and hook it up to the IAC wiring - preferably without disconnecting it from the IAC. This would give you an approximate idea of how the ECU is controlling the IAC. The green LED is for the opening-coil, Red is for the closing coil.



When you start a cold car, the ECU forces the IAC to fully-open for about a second after start, after which it slowly brings it down to partially closed so RPM is around 750 or so. You can try verifying this via the LEDs. Both LEDs might glow all the time: you should concentrate more on LED brightness to help indicate the IAC position.

Another more effective test is to remove the IAC and block both hoses going to it (I bridged them with a solid-rod to take the place of the IAC). Open up (unscrew) the black idle-thumbscrew almost completely (otherwise it will not idle). Connect the IAC to the connector so you can watch the valve open/close in real-time. Now have someone switch the ignition switch ON. On my car the IAC fully opens at this point. Next have the car started and see what happens. It should slowly start closing - but not completely. If you race it slowly, the valve should slowly close.

3. If the IAC dosn't behave as expected, and the LEDs show both coils are receiving voltage - connect a multimeter between the opening-coil and slowly open up the valve manually (eraser-end of a pencil). Check to see if the resistance stays the same without jumping (which would indicate a dirty commutator and/or bad commutator connection). Do the same for the closing-coil. If you get some wild readings, I would suggest opening up the IAC and cleaning it out (I've posted how I did this - and there are a couple of other posts on the board as well). You might want to get a spare from the junkyard before doing this...

Good luck. Getting all those gremlins out of a suspect IAC can be very frustrating !

Noel