I have read almost every single other idle thread out there and found a few similar issues, but the solutions did not seem to work for me. So when I come to a stop, my 99 XJ's idle will not settle. The tach needle bounces up and down (not by much, but its constantly bouncing). It seems like it does it worse when it's cold, but it does it when warm as well. When I come to a stop at a light, sometimes I can feel the entire Jeep shake. It runs good for a few seconds, then shakes for a few seconds, then runs good, and so on. So far, I have cleaned the entire throttle body, cleaned and replaced the injectors, IAC and TPS, ran seafoam directly through the throttle body, ran Lucas injector cleaner through the tank, replaced the spark plugs, wires, cap and rotor, and replaced the ignition coil, all to no avail. I tired disconnecting the upstream o2 sensor and running it, but that didn't seem to do much either. I'm thinking it is either an o2 sensor or a bad cat. When I'm driving down the road at any speed above 25 mph, letting my foot off the gas and just coasting results in the idle bouncing around (it comes down, jumps back up, comes down, etc.). Any input would be greatly appreciated. Thank you.

 

It is strange - normally it's one of the things you've tried! I wouldn't think a vacuum leak would come and go like that. Have you tested fuel pressure, by chance?

 

Checked for vacuum leaks yet?

 

Try this bad boy. Worked for my rumbling idle.

http://item.mobileweb.ebay.com/viewi...d=280947916638

I also replaced my rear PCV valve on the valve cover at the same time so it's hard to tell which one actually fixed the problem. You can pick a Dorman brand up from the parts store for five bucks.

 

I've checked for vacuum leaks and couldn't find any. It only has 65k miles so none of the lines are really even brittle. I have not tested fuel pressure, but it seemed more than good when I pulled the fuel rail to do the injectors. My problem is identical to this video:


Although, it is not the ignition coil as I have replaced that as well.