98 trooper high idle

Sorry for the long post, but this one is frustrating…

Mid summer, a local shop replaced the IAC (Idle Air Control motor) to fix
an occasional low idle / stall problem. As soon as we got it back, the
idle started creeping up. First about 1100 RPM, then 1500, then 1800,
then 2000, then 2200… We took it back into the shop and after much
head-scratching, looking in manuals, they told us it was the battery –
even though I tested it and it was fine (13.2V off, 14V running). I
replaced it anyway. It was idling well for a while, then started going
back up…

We took it in again, took them over a week to do basically nothing (other
than hope and pray?), said they recharged the battery again and
re-tensioned the air-mass sensor connector. Got it to idle. Its been
working ok a little longer. Yesterday it was back up to 2200, so I
started taking matters into my own hands.

I really suspect the IAC they put in is defective somehow, so I started
messing with it – took it out, put extra Teflon tape around the body where
the o-ring is. Viola! It idled perfect! I drove it around for a while,
thought I had it. But alas – I turned off the key, restarted and it was
back instantly to 2200. ARRRRRGGGGHHHH!

Anybody with ideas other than the IAC being bad before I go buy another
one? Thanks for the help.