wierd idle problem

well here goes
i have a 96 xj 4L and an auto trans
when i leave for work it idles 650-750 plus its been sitting all night and around 45deg outside, i have a 25 mi drive to work and idles great
when i go to lunch about 11am it again idles great
when i leave for home around 7pm it idles around 250-300 rpm
i cant figure it out
there is no idle adjustment on the throttle body so im stuck!!!1

Hi,
As far as I know idling is controlled by the IAC, Idle air control valve, it is located on the throttle body. I took mine off a couple of years ago and cleaned it up, it was gunged up with a black residue and it was a wonder it worked at all. I think I cleaned it with paraffin. You need to be careful dismantling it so take pictures or make notes, or you could get a new one from the Stealership. Hope this helps.

May or may not be your IAC but there is one way to find out and it's a good place to start....procedure included if you are so inclined...
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Cleaning the IAC:
1. Remove the IAC with a torx 15 driver (2 bolts)
2. Gently wiggle out the IAC from the throttle body
3. Clean the IAC with throttle body cleaner (not carburetor cleaner ) Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle as it is fragile and you can damage it pretty easily
4. Also clean where the IAC seats in the throttle body with the same throttle body cleaner
5. Consider cleaning the entire throttle body itself as long as you’re at it
6. Reinstall IAC and check idle quality

birchlakexj is on it about the iac, do that, and also check the hoses coming out of the top of your valve cover, make sure they arent plugged.