Between a place by the lake in northern Wisconsin and daily life in northern Illinois I've had my share of cold, heat, rain, snow, ice, tornadoes, floods, etc. When the wind comes off Lake Superior in January it can get a wee bit brisk. If you've been on a sled at 40 MPH in -45° you would probably remember it.
The IAT is probably clipped into the air cleaner housing or the air inlet snorkel if my memory serves me - It's been a while since I've seen a TBI up close. It should have a tan and a black wire connected to it. You can disconnect and test the resistance of both the IAC and CTS sensors. At a given temperature their resistance should compare closely to this:
The IAC is the only thing controlling the inlet air it is responsible for controlling idle speed. Since the idle eventually reaches a normal range we can presume that there are no other significant vacuum leaks which would cause a high idle.
In order to operate properly and follow the stepper commands from the ECM, the IAC needs to be clean, along with its air passages. Varnish and gum tend to accumulate on the IAC valve pintle, in the air passages in the TB, and on the rack gear of the IAC itself. It only takes about this much contamination to "kill" an IAC and cause the kind of problems you are experiencing:
The IAC can be removed, cleaned, and lubricated to restore its operation. Remove the IAC from the TB, clean off the end of the pintle and exposed parts with a carburetor spray cleaner and paper towels. Carefully apply light to moderate pressure to extend the pintle while rocking it side to side. This will force the pintle rack gear to slowly "walk" out of the corresponding rack gears in the IAC housing stepper. Close observation will reveal that the IAC pintle is NOT threaded but is a sinusoidal rack gear. If the pintle does not slowly and incrementally walk out of the housing, change the direction you are rocking the pintle by about 90° and continue trying to work it out of the housing. When you find the proper direction to wobble the pintle side to side the stem will slowly come out of the housing on each wobble. It should come out completely in about 60-90 seconds of working it side to side.
The only thing behind the pintle is the spring, so don't fear losing any small parts. When the pintle and spring are freed, clean the spring, pintle stem, and interior of the IAC stepper using the spray carburetor cleaner. Allow everything to dry thoroughly since carburetor cleaner left inside the IAC housing can have a detrimental effect on the insulation of the solenoid coils of the stepper motor. Blow it out if necessary to be sure it is dried.
Apply a couple drops of clean engine oil or light machine oil to the interior of the stepper motor through the pintle stem hole. Check the free length of the return spring. It should be at least 2-1/8" long (50mm) to have the proper tension.
If it is short, as many are, the spring can be carefully stretched and re-checked until it has a free length of about 2¼ inches.
When the spring is correct, everything is clean, and the oil has been applied the IAC can be reassembled. Align the flats of the IAC pintle stem with the key in the stepper motor, apply a bit of moderate pressure, and wobble the pintle side to side again to walk the stem back into the housing. Position the pintle so that the spring is nearly fully compressed before installing the IAC back into the TB. If the pintle is extended too far it can be forced back into the IAC when the unit is installed, breaking the rack gears in the unit.
Make sure the O ring is clean, intact, and has a bit of oil on it to allow proper seating and reinstall/reconnect the IAC. Within a few second of starting it should extend to the proper position and control idle air just where the ECM commands it.