I used a ohm meter to test the IAC, according to the Bentley manual. The outer to outer pins should read 40 ohms or close to it. the center to outer pins should read 20 ohms. Any big difference in readings, Bentley manual, needs to replace. My IAC outer pins read 41 ohoms and the center to outer pins read nothing. Not good.
Good Luck
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Sandy '83 244 DL current, '90 240, '93 850 memories

You should have three terminals on early IAC motors

I believe the to outside ones reverse the vane inside. That's with one lead connected to the center one. I do not remember which polarity goes to which.

I use a small nine-volt as it will automatically limit the amount of current to go into it. The valve gets that amount of voltage while cranking because the cars whole system drops that low. That is the same time the valve needs to open all the way.

The thunk works both ways on a car battery. A little softer with a nine-volt.

If you brushes inside are worn and the commutator is badly grooved, from lots of use, the motor gets hung up like an engine starter with bad brushes or solenoid. It will work and then not.
Only thing, you really cannot repair these little guys and there is not much to recycle either. They should be as cheap as slot car or train motors, if they were ever cheap?

This thing works every time you are off the pedal and at every start up! Its a needed thing to compensate precisely for various loads.
If the half rotational motors windings were shorting then that may have been the pop of death!

I use a small nine-volt as it will automatically limit the amount of current that go into it for a bench testing. The valve gets that amount of voltage while cranking because the cars whole system drops that low. That is the same time the valve needs to open all the way.

The nine-volt limits the wallop it will not normally get and for me, it mimics a more normal operating condition to check out a working or going bad motor. They cannot last forever.
But that just my opinion!
Phil