My check engine light is on

[tw]

Originally Posted by Undertoad

Very well, sir, we don't know what he meant by "check voltages".

'Check voltages' is about disconnecting the valve from its connector. Then measuring voltage on that connector. It says power is provided to the valve. We already know that. The valve works most of the time. That measurement does nothing to find an intermittent - only identifies a constant failure.

Moving on to what is known - new information for Cloud. IACV fully opens when the car starts. That is why a car is started without pressing the accelerator. The IACV valve does that automatically. If the IAC valve does not open, then the car would not idle at a higher rev - ie 1200 RPM. Therefore that valve operated normally when the car first started.

As the car gets warm, the valve remains mostly closed. But if a warming valve gets stuck, then the car will run rough (too lean) until that unpowered valve eventually frees itself; and closes.

Of course a fully depressed accelerator would make that stuck valve ‘not apparent’. So yes, what is done to make ‘roughness’ no longer happen would be a critically important symptom.