[ChevyTech]

I still think it is possible that the IAC is not working well.
When started, the RPM should raise, and start to slow down as the engine runs.

After the engine is shut off, and before it is started, the IAC should open somewhat. When the engine is cranked, and if the IAC does not open at all the engine will usually “load up” or “flood.

IAC passages can get plugged up with carbon or muck. The IAC units get erratic as they get old and stick. Use care when cleaning the IAC. The IAC should not be cleaned with carburetor cleaner or other harsh chemicals. If the chemicals get down inside the IAC, it will damage it.

To clean the IAC, you should remove it, and use a wet rag to wipe the tip of the plunger, while holding it with the plunger pointing DOWN. Be careful, the IAC will break easily. It is aluminum. Clean the passages in the TBI unit while you have the IAC removed.

You can remove the IAC to clean out the passages in the TBI, but use care, the IAC can turn very hard and you could damage the IAC removing it.

I do not suggest unscrewing the pintle (plunger). If you don’t get in back in far enough, the IAC can get damaged if the “pintle” (plunger) bottoms out in the TBI, when you screw the IAC back in.

Usually the IAC does not go bad electrically, but it is common for them to stick and stop moving.

The IAC is a stepper motor and uses short pulses of electricity on the wires to move its position.

If the IAC sticks as does not move as it should for each pulse, the IAC count will get off because the computer does not know the actual position of the IAC, but the ECM tracks the commands it has sent to the IAC and assumes it has moved every time it has been sent a pulse.

IAC testing:

Terminals A to B should be 40 to 80 ohms

Terminals C to D should be 40 to 80 ohms

Terminals A to D should be infinite

Terminals B to C should be infinite

I suggest only using a digital (high impedance) ohm meter for doing these tests.