Hello, I tried searching for this questions but could not find any threads related to this problem. I recently bought a 2000 XJ with 180K miles - but it looks like it has 50K miles. It is in amazing, clean and original condition. Recently I noticed the engine will rev up about 100-200 RPM exactly every 5 seconds, then go back down to a smooth idle. It is like clockwork. Runs great otherwise. You can hear something kick on when the engine revs up. I did an oil change, air filter replacement, oil filter and cleaned the IAC tonight to see if that would help. It is still doing it.

Check out the here: and here: .

Any idea what is going on? It is so weird.

Any help greatly appreciated. Oh - additional info: the other day I removed some aftermarket lights that were not working from the bumper. Not sure how that would play in but thought I would throw that out there.

Thanks,

 

Is your airconditioner working when this happens?

 

No, the AC is not on.

 

Probably isn't it, but as a general course of troubleshooting, you might look down inside the throttle body and see if there are deposits in there, and on the butterfly and backside of the butterfly. When it's closed if it isn't getting the right amt of air sneaking past the butterfly, it might goof up what the computer is trying to do. Clean with gentle action using a brush and carb cleaner (no hard instruments or screwdrivers!). There might also be a tiny hole open to the IAC that could still be plugged with deposits.

Also, might be a good idea to remove the EGR and clean under it with carb cleaner. They also can get loaded up with deposits. In addition, listen for vacuum leaks (high pitched hissing). If you can put a vacuum gauge on it, see what it's pulling for vac. Could be a cracked line or connector..

 

Pull the throttle body off and thoroughly clean it with some throttle body cleaner, also unhook the battery when you do this, when you reinstall it and hook up the battery it will go into a relearn mode and that may fix it. I have solved idle issues on several Mopar vehicles of that era by doing this. No EGR to worry about on a 2000 model, I believe they got rid of EGR on the 91 models.

 

Guys - I am pretty sure I figured it out thanks to the help of emx72. The AC was not "on" rather the temp setting was not all the way on red - like in the light red section. That comment got me thinking about the AC compressor - and I remembered that I did see it spin up when I started the engine for the oil change. So I ran back out to the jeep, turned the heat to all the way hot - the revving stopped! Nice smooth idle. So I looked around and found this thread: https://www.cherokeeforum.com/f2/ac-...m-fixed-96628/ which talks about the refrigerant being low, when ac running causing pressure to drop after compressor turns on, so it turns off. Then on, and of and so on.

I ran to auto store, got a recharge kit - about to test it. Will let you know if that 100% fixes issue but I am confident it will. I am thoroughly impressed with the amount of knowledge here!

 

YES! Totally fixed. Thank you all, especially emx72 for pointing in the right direction.

 

I'm glad it worked out.

 

Most people don't realize the A/C is designed to run in Defrost to keep the refrigerant seals conditioned in the winter when it's not being used. Before they made this change, you usually had to recharge the A/C every spring. SO, the rpm is designed to increase with the added load of the compressor. If you don't want the A/C to work, simply unplug the compressor clutch.

 

Glad it worked out. Thanks for explaining the issue for the benefit of others. Still, take a look inside the throttle body and clean out any deposits. Also check the contacts on the underside of the distributor cap for boogers. Those are just common issues which can contribute to operational issues. Good catch on the EGR removal.

Mark

 

Will do - thanks!