Most likely it is the IAC. You could try unplugging it and then start the engine to see if it makes a difference. The other way to test it is to remove it and see if you can blow air through it. No air should pass through.
If you decide you need to replace it, most aftermarket (Borg Warner) won't work because you have to mount them backwards 180 degrees. [I kid you not] Due to the placement of the oil filler tube, it can't be done on the SC. You will need the motorcraft part from Ford, or a type which has the valve closed when its not hooked up.