Viewing Ford IAC Solenoid signal's
Here's some insight on Ford's IAC used on most all Ford model years and makes with fuel injection. These images show how the PCM adjusts ground level to the solenoid to keep idle speed at a computed value. As loads on the engine are increased from air conditioning, engine cooling fan, accessories loading the alternator, or automatic transmission being put in gear, the PCM adjusts for each added load.
This image shows the engine at operating temp, idling in park.
As each load is added, ground level is increased, and more air is bypassed to keep idle speed normal.
Watch Minimum volts get closer to ground as each new load is added.
Here it's at 5.48 volts, This was the Air conditioning being selected.
Automatic transmission in drive...
All remaining accessories turned on.
96 Ford Ranger 3.0 V6 IAC at idle engine at OT