Do I have this right..... if things are normal, you should feel the Idle Motor (IAC) casing vibrating (like a cell phone) with the motor at operating temperature, and the engine "idling" (no pressure on the gas pedal) ?

My IAC is Bosch, with a 2 wire connector.

The car will idle at 800rpm, until it warms up to operating temperature, then it idles steadily at 1100rpm. If I shut it off, then immediately re-start, Idle is back to 800 rpm.

I've cleaned the IAC, it does move freely now. Previously it would occasionally idle at 1100 rpm, post-cleaning it now consistently idles at 1100 once the engine warms up.

If I test the IAC motor out of the car, does the 12v polarity matter ?

Rgds, D.