Direct copy of a post I have on 3si for testing the IAC
You can test it while on the car.
All you need is a multimeter.
Test the continuity across the pins. There will be six pins, 3 in each row.
123
456
Test continuity across pins 1 and 2, pins 2 and 3, pins 4 and 5, and pins 5 and 6.
Continuity should be around 28-33 ohms if its an old style beige ISC.
If you get no continuity between any two pins then the ISC is shot.
If you find out yours is bad you can get one at rockauto.com
More Information for STANDARD MOTOR PRODUCTS AC99 Its part number AC99