High Idle When Hot.

[jeepboy381]

So here's what is happening, it's kind of weird. I have a 1987 4.0 5 speed, it has all the renix sensors but the H.O. block, head, intake, and throttle body. It alway's idles at 750rpm when cold but once I have been driving for 15 minutes and it gets up to operating tempurature it will idle around 1,000 to 1,200 rpm. I would have to say that half the time if I put my foot on the brake and let the clutch out while its in gear and let the rpm's drop down to under 500 then take it out of gear, it will either idle a little lower or drop right back down to 750 rpm. The other half of the time it will just continue idleing high, any idea's? All the sensors tested out fine, can't find any vacume leaks. What would heat have to do with this? On colder days when the engine runs cooler it rarely does this!! I will never buy a 87-90 XJ again, there are way to many wires and it is a mess under the hood from the factory. I like my 97 cherokee much more even though it is stock. Under the hood it is nice, neat, and easy to work on. Thanks Josh

[jeepdude10000]

u know if u search more u will find info on this on many treads, its kinda late ill think of it later.

[jeepboy381]

I know and have done this, my TPS is new and adjusted properly, my idle stepper motor is functioning, my MAT, Map, and CTS all are working fine. No vacume leaks. I have never heard of this happening before, "half the time if I put my foot on the brake and let the clutch out while its in gear and let the rpm's drop down to under 500 then take it out of gear, it will either idle a little lower or drop right back down to 750 rpm. The other half of the time it will just continue idleing high, any idea's?" Just woundering if anyone else has some idea's?

[corbinafly]

You say that your IAC motor is good, but is it clean? They can get stuck if covered with too much carbon/crap.

Kyung