90 4.0 L idles high

I've got myself a bit of a problem I can't seem to figure out here, I've got a 1990 4.0 L - standard tranny that after it warms up and is driven a bit (5 - 10 minutes) the engine starts to idle high, between 2000 - 2500. I've tried the obvious, cleaning the throttle body and changing out the throttle position sensor and the idle stepper motor, when the engine is idling high, the throttle body is in the fully closed position. I can't figure what I'm missing, I would say it was a vacum line, but it doesn't happen all the time, just after the engine is good and hot.

Any guesses, thoughts or direction would be greatly appreciated,

Thx

The wifes 87 would idle up after it got hot, found some of the intake manifold bolts, were less than fingure tight.

These Renix MPI's do that and I'm not 100% sure why. You already checked/cleaned the main things but here's a couple more:

Obviously the manifold bolts and spray WD-40 while running around the sealing area to make sure you have no leakage there.

Wiggle and check all connections to ECU under the dash. Sometimes when mine does this, I kick the bundle under there and it settles down.

Also, next time it does this try checking the latch relay w/DVM to make sure it's energized properly. Oh, and the well-worn ignition switch on mine sometimes doesn't return/switch fully from the start contacts so the ECU still thinks the system is starting and forces the IAC to full open position.

Finally, go through the couple temp sensors w/DVM. Qualify and repair any suspect wiring. The connectors on my '89 aren't the most reliable I've seen.

Oh, almost forgot - often the problem can be the IAC itself because the ECU parks it in open position for next restart. However, if it's really hot it make stick inside the TB port and not be able to retract. Especially if the o-ring was buggered during installation the IAC isn't very square in the hole and this can be a problem. I don't like the quality of IAC's I've gotten through Kragen/AZ either. I've heard of a Holley performance IAC that's supposed to work with Renix and I'm tempted to try myself.

I found the Holley info -

*** cowboy_emt_xj on J.U. posted that "holley part #543-105 is an idle air control motor for holley's pro-injection system," and is a direct swap for this part for around $28 at AutoZone vs. $125+ at the dealership!

Check the manifold vacuum. Vacuum leaks are the biggest cause of high idle.

as things would have it, it was indeed the manifold bolts, all of em were finger tight, so you can only imagine my surprise at that. I torqued em all down again, and life is good, engine runs like a dream now.

Thanks for all the help! I may probably would have hung myself in the bathroom before I bothered to check that out.

Cheers!