High idle

I have a 1989 4.0L.I have two issues.First, After driving it,sometimes it has a high idle '' 1400 +- rpm''. For the rpms to go down I need to turn off the motor and sit for few minutes then start it back up, I sometimes need to do this several times. Second, It has developed a miss while driving down the freeway. It will be running great and then it will just miss and keep missing. One thing I did noticed is that the rpms or jumping a little at idles. Any help would be great......

Idle miss is usually ignition. Then the ignition breaks down again a higher RPM's (usually above 3000-3500 or even higher)

Bucking at freeway speeds, at operating temperature, is often an O2 sensor. Usually around 2000-2200 RPM with a steady throttle or mildly accelerating. A bad O2 sensor that is causing bucking also seems to lower your red line way down.

1400 RPM idle is usually a vacuum leak. But can also be a TPS or even a sticky IAC.

Vacuum leak can be anything from the vacuum tubing, vacuum canister behind the passengers side front bumper, to loose manifold bolts.

TPS is often water inside the TPS or poor grounds.

Just some possibilities.

The search feature of this site is your friend:roll:

User cruiser54 is The Man when it comes to your Renix XJ. Please read his Cruiser's Renix diagnostics thread.

My jeep suffered from the same problem. It was a combination of a bad TPS and poor grounds.

Please read the above thread. Welcome to Naxja!