Originally Posted by dirtyjerz

sounds like your having the problem I just had and it was the map sensor that controls iac and vacuum lines mine was intermitten for a while with a rough idle occasionally until it got locked on full throttle and tripped a code

Originally Posted by timamybrown

Make sure your dizzy cap is still tight. Mine came loose and I had the same problem it didn't ideal bad but you could tell something wasn't right. And it ran fine at speed.

Originally Posted by freegdr

When was last tune up performed ? Start with basics there cheaper than replacing and thinking parts will add up to.

Originally Posted by McGeeXJ

Define "tune up", as far as I'm concerned I am past covering the basics.

Originally Posted by cruiser54

Plugs, wires, cap and rotor every 30,000 miles and a good throttle body and IAC cleaning.

Originally Posted by McGeeXJ

I've checked the other rough idle threads. Everybody has a different setup or different symptoms. Today I got an obd2 scanner. One of the ones that you can connect with the wifi signal to a third party app on your iPhone. I just want to know what's up with the idle on my xj. So far I've done the 784 injector swap, new plugs, wires, dizzy, rotor, and new air filter, I even started running better fuel. It doesn't really feel like it is missing, and it isn't consistent, but the jeep vibrates a hair when the rpm dips. It is only at idle, and while playing with my new scanner I found that if I slightly give it throttle the vibrations go away and the rpms evened out. I'm talking about just the slightest amount of throttle, still below 800 rpms. Somedays the symptoms are worse than others but there has never been a common condition that would cause the problem. The only thing I can think of is the xj's heat soak issues. I still have this problem no matter what the temperature is outside. Recently I opened the hood and let it idle while at operating temp to see if it helped. It seemed like it did a little, but the problem still seemed underlying. I should've threw a box fan on top of the fuel rail to further troubleshoot but I didn't have time and I figured that it was cool enough out that it wouldn't matter if I had the fan. What do you guys think? Should I play with my idle, explore more into the heat soak, or try a different route?

Here is a screen shot of my xj idling for 30 seconds at running temp. It bounced around between 710 and 740.