Initial Setup of TBI, TPI and MPFI systems. Min Air Adjust, TPS set and Fuel Pressure

[FSJ Guy]

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.

[RobertISaar]

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.

[EagleMark]

I don't know what I did the first time I had one out of TBI unit on my test bench but when I turned system on... or jumped A and B on ALDL it came flying out! There was no tiny movement!

[RobertISaar]

that would be the IAC reset function of the ECM. it pulses the IAC at either 80 or 160 Hz (or at least it does on later systems) to fully extend/retract/whatever.

obviously, it's not a single pulse that does that.