The Idle Air Control valve, commonly just called the IAC, is a servo motor controlled valve that helps maintain the engine at idle according to the demands of the engine control unit (ECU). Given that my engine was having a hard time idling for more than a few seconds a failure here would not be surprising. I had already taken it off, so I figured I’d get it on my workbench and poke it a little to make sure it’s still working as expected.
The IAC is a pretty simple device. It’s a tube with a servo motor inside that opens and closes a valve to control airflow into the intake manifold. How far open the valve is depends on the voltage supplied. 12 VDC should open the valve up all the way. I also referenced the Volvo “green book” on the intake system and found that the resistance across the two input terminals should be 8 Ohms. So those are the two tests I performed. I’m happy to report that my IAC is just fine. It wasn’t difficult to test, but just in case here’s a video to illustrate how I did it.