Finally got to replace the IAC on a friend’s car, and the car idles perfectly now. Before, his car would rev from 1000-2000 RPM. It got progressively worse, and started to rev from 1000-4000. It even revved up once all the way to 6000 and held there until he pushed the gas.
The install itself isn’t really hard, just a bit tricky due to the coolant hoses, and the tight space to work in. I would definitely advise doing it when the car is cold, since coolant will come out no matter what you do.
GT-S IAC and gasket (not sure if GT’s is the same):
Tools For Method A:
Vise grips (2)
Small socket wrench with philips head bit
Tools for Method B:
Socket wrench with 12mm socket
Philips head screwdriver
IAC valve itself: