So: on my 90 240, I suspected that my idle air motor was not engaging; the idle was always a bit low. I tested it; it was fine, but if I unplugged it, there was no change in idle.

Per Bentley, I next tested the terminal #2 of the TPS for continuity to ground at idle (which is what energizes the idle motor, yes?); no continuity. Must be a bad TPS, I think, so I replace it. Still no continuity to ground at #2.

Here's where it gets interesting: I unplug the TPS. I disconnect the throttle linkage. So now, the throttle valve should be closed and no way the idle control motor is working, right? The car starts and idles fine.

Next, I unplug the MAF. The car starts and idles fine!!! Per Bentley, I test the MAF. Tests as it should.

Other than a low idle, the car has been performing at it should: starts instantly, good power, cruises at 80 mph all day.

I'm stumped [8D]

 

If the throttle body is not adjusted properly then the switch will not function properly either.
The TPS should click when you bairly move the throttle. If not then the switch isn't adjusted properly not allowing the idle motor to work.
Also if the rod is misadjusted then the switch might not be working either.