weird high idle
 

Ive got a 4.0 xj w 255k, just replaced the pressure regulator/filter on the pump. starts better but I've still got a just ridiculous idle problem. its subtle and but its infuriating. Cold start it usually has a idle at about 1100, if not it starts and runs at the regular idle, it never does the high idle to regular idle like normal. When its at running temp, it usually starts at the regular idle, so good, but then when I get to the first stop light, its pulling hard to try and stay around 1100. usually when I leave from the stop light, you can feel the idle pick up to around 1100 and w no pedal it will go 25mph, will even shift into 2nd. Again its intermittent, and when this is happening I can left off the throttle running anywhere from 35-55 and the thing will hold speed or slow down REALLY slowly. When trying to come to a stop it takes a lot of brake and the wheels really have to fully stop for the idle to come down to 850. I believe the idle to be set correctly at 850ish. I did put an HKS throttle body on it, but I even replaced all the sensors in it when I did. With Mopar ones. I think this is when it started happening but idk exactly when it started. The old throttle body looked like ****, and that thing was expensive and I can't tell where any part of it was messed up or cracked or doesn't move correctly. So I took to a very solid mechanic shop, they put new valve cover breather pieces on there and said they don't know. It doesn't have a vacuum leak, I know cause all that **** is new. Except the brake booster but.
Other times it drives around great. Idles perfect at the stop lights and in the driveway. Then you can start it up and it goes back up to way to high idle. I will also say it cold starts better now w new psi reg.
Any help be great appreciated, can post pictures of whatever if needed as well.

It sounds like a bad IAC, or you've got an intermittent vacuum leak. Check all the hoses, and try pinching off the line to the brake booster and see if the symptoms improve. Looks at the wires to the IAC carefully too.

Aliright ill give that a try. I did install a new connector on the IAC and the TPS harness side so ill check those crimps.
Thanks

Man its so weird. I really want to believe its the IAC, even tho I put a new one in it, maybe I messed it up. I did a pull test on the wires, didn't effect it, and my ecu grounds seem ok. Cleaned them not to long ago. When it starts, its around 950 usually, like its in that start high idle, but then it creeps up for some reason. Almost like its wired up backwards. I also forgot that it doesn't seem to adjust to the A/C at times. If it is at regular idle, the a/c will drop it down a bit to far. Maybe it is the IAC. obv it will be the 185 dollar one

I had the same problem. No codes. Infuriating is right. When I started to take a closer look with a scan tool, my main 02 sensor was very lazy and slow. At first I thought it was the scanner I was using because the pattern was normal, but abnormally slow. A new main 02 resolved the issue. If you have access to a scanner you might want to take a look. I to removed my throttle body and IAC, then cleaned everything meticulously with no results. And yes I know it sounds crazy. An 02 sensor for a intermittent high idle/surging issue. I’m not saying throw an 02 at it, but it might be worth looking into.

Had a similar bug. Idle would go up to 1000 rpm in drive whencar was stopped. Also 1000 when in neutral and park. Had a bad map sensor. Sometimes motor would oscillate between 750 and 1000. Put in new iac, tps, and vss. Finally got a map sensor that would fit onto connector. The first two from China wouldn’t go on the connector. Got one from eBay that was used but it worked like a champ! Good luck.

Belay that last! Problem came back after a few days. Still trying to figure it out.