Quote Originally Posted by FSJ Guy View Post
If the IAC motor is a stepper motor (and I think it is), GM probably doesn't want techs to simply apply straight 12V to the coils and then think it's bad because nothing happens. A stepper motor has to be fed a specific type of signal in order to make it move.
pulse it at an 80Hz frequency with 12 volts and it will move as it is supposed to. i imagine the average tech (at least back then) wouldn't know what to think of a little IAC motor that moves an almost invisible fraction of an inch when power is applied, then when they remove power and reapply, the same tiny movement.