MNOE

I've had this issue for awhile now and cant seem to get it taken care of. It's throwing codes for misfires and is stumbling badly while at idle or in drive or reverse without the gas pressed. As soon as it's pressed you cant feel it. it has new coils, new plugs, I cleaned the throttle body, the throttle position sensor as well as changing the camshaft position sensor today. That seemed to help for a few mins but after a few re-starts and a trip to the store, bam, it does it again. What am I missing? Any suggestions?

dave1123

Check all your vacuum hoses for cracks, especially the MAP sensor. My trick is to use an UNLIT propane torch with the valve just cracked open and play it around the suspect hoses and gaskets. If there is a leak, it will pull in the gas and speed up the engine.

MNOE

Im more than willing to try anything at this point, but why would it run smooth after I changed the camshaft postion sensor then go back to misfiring again? It seems like everytime I remove the battery it resets and is smooth for a drive or two then the issue starts again

dave1123

The only thing I can tell you is when you disconnect the battery, the PCM looses all it's stored data about your driving habits and relies on factory pre-programmed info on it's chip. After a while, the PCM relearns your power demands and driving style. It uses data from all the sensors to set up these parameters in it's memory. It seems to be getting mixed signals from somewhere.

MNOE

Would a crappy battery cause this issue? I don't know if it's related but the guage fluctuates a little while idling. i also thought that maybe it was worth looking at or changing the O2 sensors, or do you think it's still might be a vacuum leak issue?

rangermonroe

Why unlit?

dave1123

Because you want the gas, not the flame, idiot! I am stunned you had to ask that question.

MNOE

Well I tried a vacuum test but used brake parts cleaner, didn't have any change in idle that I found. It is however now only throwing one code for the last day or two, rather than the four I think it was before. Now its only a misfire code for cylinder one.

rangermonroe

No clue then. I am here for the info.

The problem with using brake cleaner is that it's low volatility compared to gas. The gas will not "persist" in one place, and can allow you to pinpoint an exact spot. Also, the reaction is closer to instant "on/off" when applied to a leak.

Also, brake cleaner might degrade the rubber and plastics of the underhood components. Propane will not.

(the above is not directed at you OP, but to those who are just learning this stuff and have found this page through the googles and such).

MNOE

Yea the thought crossed my mind while doing it, maybe brake cleaner was a little abrasive for rubber and things, oh well, live and learn. I've ordered 02 sensors last night and will give that a try next, as well as re check the plug on cylinder one. Maybe ill try swapping the coil to another one and see if the problem follows.

dave1123

I hate asking this question, but WHAT YEAR 4.0 are we talking about? I only got the "4.0" from your signature, and are we talking about a Cherokee or a Grand Cherokee? Also, your location is important so we know what kind of environment this problem is occurring in.

Sorry, but I get so wound up when I have to pry the simplest info out of a poster. As you can tell, I'm a good diagnostician but lack good customer relations qualities.

MNOE

Oh sorry about that, I thought I had it in there. It's a 03 grand Cherokee Laredo. I'm in Florida.

dave1123

Sorry I went off on you. You DID have your location on there, I just didn't see it. Most people just put "Cherokee" in their signature and it sets me off on a tirade. The XJ is a totally different animal in some respects.

You do realize the coil pack on your WJ is an expensive item, don't you? You might want to check the spark plug insulator boots behind the coil pack for carbon tracking and deterioration. I bought a complete Denso set of 6 boots and springs for $12.77 from rockauto.com. That coil pack is $60 to $125.

MNOE

Hmm, i'll have to take a look at that. The coils were all new when I got it from previous owner, so I assumed that part would be included with the new coil (I've never replaced one obviously lol).

dave1123

Okay, now that I know what vehicle you've got, go to wjjeeps.com and learn about it. There's enough info there to fry your brain!