I'm new here, so bear with me. I've searched far and wide for a solution and could never find anyone with quite the same problem so I'm hoping you guys here can help out. So here it goes...

I picked up a 99 XJ last spring. About August last year, I started having bad rough idling only when it was rainy out. Got a CEL code pointing to rear O2 sensor, changed it, and the rough idle was much better, but it was still a little rough and not weather dependent anymore, so I figured it's an older jeep, nothing to worry about (bought at 111k).

About 2 months later the rough idle came back again, and CEL codes pointing to Cylinder 1 misfire. I checked for vacuum leaks, nothing. Changed the plugs, wires, cap, rotor, ignition coil before it finally seemed almost normal again. About 4 weeks after that it came back, I changed the plugs again, and it fixed it. However, the first two plugs seemed a little more worn (white chalkiness). It seemed like the jeep was eating through plugs so I just kept changing the first two every month or so when it would get rough enough to put out codes. Eventually it got to the point where my band-aid solution wasn't cutting it. I've tried a new TPS, coolant temp sensor, new fuel injectors...no fix.

Eventually I couldn't start the thing without having to give it gas, AC stopped blowing cold air, and my coolant started to get dark brown and started to disappear on me. But I was still getting just over 18mpg highway (was over 19hwy when I first got it). After further research I concluded head gasket. Called my buddy up and had a blast taking the head off and discovered it had three cracks between the valves on cyl's 1,2, and 4. Grant it, this was a 0630 head. I've never heard of these things cracking, and I haven't let the thing overheat since I've owned it. So I pulled one from a junkyard, sent it to a machine shop to get cleaned up, resurfaced, valve job, threw the new head on and she ran like a champ for the first time since I bought it. The coolant hasn't gotten brown or oily since after a bunch of flushes. The whistling sound it used to have went away too.

About 100 miles in I noticed the rough idle starting to come back, which I guess is telling me that the computer is learning something wrong from the sensors...but what else is left? CPS? MAP? IAC? PCM? I can start it fine unless after I run it at operating temperature, then it just stumbles before it starts up after cranking for a little while. The transmission seems to shift a little harder and weirder, but I think I just need to adjust the transmission pressure cable as the FSM says.

The only things not stock are the injectors (did the four-pinhole upgrade, the Neon ones) and the intake is an AEM "cold air intake," in case anything could be from that.

Any suggestions? What else should I be looking for? I'm officially stumped. I know it's a long post, but the story seems to be different every month or so...

 

my 99 would stumble when it would warm up after stoping at a store for cup of coffee and then get back in and start going and it would stumble.i change the front 02 and have not had it happen again