You got the jest of it there!

As long as the throttle body is clean and the plate is "just" resting against the stop screw (bacically shut off) it should idle low and may even stumble when the idle motor is grounded. The stop idle screw is there only because of machining tolerances. A fixed stop can not casted exactly in relationship to the bore diameter and plate pivot rod fit up.

After the by-pass air adjustment (the black knob) for the slower idle. Disconnect the ground and the engine will rev up a touch.

The engine should rev up slightly each time it is started. Just past its idle point then settle back to a smooth idle as it was set for but again higher than grounded idle because the idle control motor is now centered.

It is being adjusted to the program in the ECU because the throttle switch, is saying to the ECU, "I'm closed and want to idle".

Hope this makes it a little more clear for you.