Surging Idle

I have a '00 XJ with the 4.0 with about 60K miles on it. When I start it up the idle surges from about 700 rpm's up to about 1200-1300. It then goes up and down every 5 or 10 seconds. It also sounds like a fan or compressor is turning on when it revs up. I would assume this is part of the warm up feature but it doesn't shut off for a while.

Once the engine warms up the surging stops but the fan/compressor continues to turn on/off every 10 seconds regardless of the temperature. Does this sound familiar to anyone, and if so is it just part of the warm up feature or is there something going on?

Are you running the A/C or defroster? That can cycle/run the compressor.
It puts more load on the engine so your IAC will compensate by speeding up the idle. It also turns on the electric fan. If you don't have any accessories on and it still does it.... there's a problem.

It is normal for a engine control to speed up engine idle for the defroster. My buddies 82 buick did that in college. It takes more power to turn the compressor, but I don't think my 88 XJ does that.

I think you may need a throttle body cleaning. The idle air controller may have crud making it stick. The sticking makes it slow to resond and it gets into cycle. It costs me 1.0 hours labor at the dealer to have them clean the throttle body and check over the entire engine operation. They remove the throttle body form the manifod, clean it and reinstall with a new gasket. It some of the best money I even spend on the XJ. I had the throttle body on my 86 Ford Mustang with the 302 (5.0) V-8 engine cleaned every 30,000 miles. I'd get the idle changing at the worst from 800 to 1500 then to zero. I condiser throttle body cleaning just a routine maintenance thing, just like enigne oil and air fitlers.

If you don't have a mechanic who knows you then time to get to know one. I find you get better work if they know who owns the vehicle vs being the next one on their list to fix.

I had in my 03 Buick le Sabre to the dealer for rotation and balance. I did not get the normal mechanic I use and they guy gave the car back to me missing a valve stem cap. It was missing when it came in but you'd expect attention to detail at the dealer. The customer service lady called me to see if i had a good experience, I told her how they messed up. Long story short they did make it right BUT if I had the guy who knows me he would of repalced the missing cap while he rotated the tires.

My 01 is the same, it's the AC. If you turn your heat/AC switch all the way to the left it should stop.

Problem solved, it was just the compressor running because the defrost was on. Should have figured that out.

Thanks for the advice