Pull the IAC idle air control valve handle out fully using the IAC actuator.
Start the engine. If the idle speed is above 800 rpm:
- find and repair vacuum leaks;
- check for sticking throttle or not closing tightly enough;
- check that the basic idle speed parameters are set correctly.
Inspect IAC lines for blockages.
Measure the resistance between the terminals of these IAC valves. The resistance between terminals C and D. A and B should be (from 40 to 80 Ohm).
Check for an open or short in the wiring between the following terminals:
- terminal D of the IAC valve connector and terminal A28 of the ECM connector;
- terminal C of the IAC valve and terminal AZO of the ECM connector;
- terminal B of the IAC valve connector and terminal A13 of the ECM connector;
- terminal A of the IAC valve connector and terminal A29 of the ECM connector.
The article was borrowed from the website «CHEVYMAN.RU»