1. Turn the engine off and allow it to cool down.
2. Locate the idle air control (IAC) valve. It is usually on the throttle body or near the air filter housing.
3. Check the AC compressor belt tension. Using the proper size wrench, turn the tension adjustment bolt clockwise to tighten the belt, or counterclockwise to loosen it.
4. Make sure that the throttle position sensor (TPS) is properly adjusted.
5. Once you have confirmed the condition of the IAC valve, tension adjustment bolt, and the TPS, start the engine and let it warm up to normal operating temperature, with the AC turned off.
6. Turn on the AC and observe the idle speed. It should be between 650-700 RPM.
7. If necessary, adjust the idle speed using the idle speed adjustment screw, which is usually located on the throttle body.
8. Turn off the air conditioner and check the idle speed again. It should be at the same RPM as it was before you turned on the AC.
9. Repeat steps 6-8 as needed until the idle speed is correct with both the AC on and off.
