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Rough Idle, Occasional Misfire, CEL

A

alopeks

NAXJA Forum User
Location
D/FW Metromess
Sorry in advance for the novel...

1999 XJ Sport, 4x4, 4.0, auto, 176K
Purchased in November, from a dealership in North Texas. Jeep was last owned by one of the Service Techs there, and was his teenage daughter's. He told me about a couple outer minor things, but mentioned nothing about any engine issues.

Noticed the idle a little rough about 2 weeks ago, and suspected vacuum leak or O2 sensor issue based on previous 99 XJ. Couldn't find leak anywhere, and sensors both checked out. Hadn't misfired or popped a CEL yet, so just tried to be careful. Few days later the CEL, and AutoZone pulled the code as P0455 - Large EVAP leak. Think I tracked down the source, but not sure, and it hasn't stopped the idle issue.

Later I started getting the misfire, VERY intermittently. Usually happened under hard load/acceleration, but still rarely. Vast majority of the time it didn't stumble at all. Threw another code, this time P0303 - Cylinder 3 Misfire Detected. I've read about the common vapor lock issue, which I never experienced in my old XJ, but I don't know if that one had been serviced/heat shield installed by previous owner. Doesn't look like there's heat shield on mine now. Question is, the misfire issue isn't necessarily following heat soak condition of the vapor lock issue. What I've read online indicates that this should happen more consistently based on short trips/warm engine starts.

AutoZone's system (I know, I know...) said most ASE mechanics would recommend checking crank position sensor. Looks like might a replacement based on connector style, but seems like the issue would be far more consistent if that was the problem, right?

I found a description of TSB 180100 that says there's a false code of misfires and EVAP leak, but I can't read the full text without buying it from some 3rd party source. I'd like to avoid that, since I can barely afford to keep gas in it at the moment...

Also, anyone know if Jeep will still install a heat shield, if that's the issue?

Again, sorry for the novel...

-alopeks
 
Haven't seen anything unusual with the plugs, wires, or injectors. Doesn't mean there isn't something wrong, I just haven't seen it...

-alopeks
 
Don't assume the mechanic kept up the maintence. Inspect/test all the tune-up parts, including the coil, or install fresh tune-up parts. Add some fuel injector cleaner to the gas, clean the throttle body and the idle air controller. Fondle all the wire plugs and make sure they are tight. Clean and snug all the ground connections and the battery connections.
 
Not assuming anything. I know it received a tune-up when I bought it, because they also did a radiator flush, which later exposed a very small crack on the passenger side of the radiator. I've been keeping an eye on that as well.

All the plugs look good, wires look good, and distributor seems to be functioning normally. Drove this morning about 20 min, mostly on the highway, with no issues except a tiny rumble of the idle. Left Church about 2.5 hours later and saw the same, but just drove down the street to meet family for lunch. Left 1.5 hours later, drive back home for another 20 min and didn't have anything unusual until I was off the highway, when the idle got really rough again. Sitting at a stoplight the rpms were jumping between 650 and 900, and every few seconds hitting 1000. Normally, it sits right at 850/900 and purrs like a kitten. 5 min later it sputtered a few times, just as I was parking in the driveway. That's why I've been suspecting the heat soak/vapor lock issue, it's just been so unpredictable about it. Supposedly it's more our an issue on warmer days, and that hasn't seemed to have been the case.

BTW, the CEL went away a couple days ago and hasn't returned, but nothing was changed in that time.

-alopeks
 
These guys are trying to help you and the least you can take the time to listen.20.00 and 20 minutes to change plugs and you can probably close this thread.I'm an old man and i look good,but very little of me works good anymore.:dunno:Or you can keep on asking and sooner or later no one will listen.:idea:
 
alopeks said:
Sorry in advance for the novel...
I found a description of TSB 180100 that says there's a false code of misfires and EVAP leak, but I can't read the full text without buying it from some 3rd party source. I'd like to avoid that, since I can barely afford to keep gas in it at the moment...
Click to expand...

I can read TSB 18-01-00... :greensmok I'm not gonna post the text here because the admins don't like that, but basically, all it says is to check your vacuum lines for kinks and pinches and stuff before replacing your leak-detection pump if you come up with a P0455. I had a similar issue a while back, Jeep would sometimes randomly start misfiring at about 1,500 to 2,000 RPM, (but not above that, oddly) idle would fluctuate all over the place sometimes, no real codes to speak of (except for a CPS/CKP code that would come and go.) Replaced the CPS with a factory pick-up coil (Thanks OMIX-ADA! You basically had one job when you built that distributor...) cleared that code up no problem. Replacing the front O2 sensor with an NGK or NTK or whatever they want to call themselves this week cleared up the misfire problem. Runs great now.
 
Bobbie,
What did I say that sounded like I wasn't listening?

I pulled the spark plugs, none of them are fouled, cracked, etc. I made sure they were all gapped to spec. All the wires are new, seated properly, etc. I don't see any arcing anywhere, I've inspected all the vacuum lines and used engine starting fluid to search for leaks, checked all the grounds, pulled and cleaned the fuel injectors, added injector cleaner to the gas, made sure every connector I can find is seated properly, and inspected all the evap lines. I replaced the only rubber connector that was brittle, and I'm at a loss for the other symptoms. That's why I came here.

-alopeks
 
alopeks said:
Bobbie,
What did I say that sounded like I wasn't listening?

I pulled the spark plugs, none of them are fouled, cracked, etc. I made sure they were all gapped to spec. All the wires are new, seated properly, etc. I don't see any arcing anywhere, I've inspected all the vacuum lines and used engine starting fluid to search for leaks, checked all the grounds, pulled and cleaned the fuel injectors, added injector cleaner to the gas, made sure every connector I can find is seated properly, and inspected all the evap lines. I replaced the only rubber connector that was brittle, and I'm at a loss for the other symptoms. That's why I came here.



(Plugs & Wires look good) I have see brand new plugs out of the box that were Bad.

-alopeks
Click to expand...
 
alopeks said:
All the plugs look good, wires look good, and distributor seems to be functioning normally. Drove this morning about 20 min, mostly on the highway, with no issues except a tiny rumble of the idle. Left Church about 2.5 hours later and saw the same, but just drove down the street to meet family for lunch. Left 1.5 hours later, drive back home for another 20 min and didn't have anything unusual until I was off the highway, when the idle got really rough again. Sitting at a stoplight the rpms were jumping between 650 and 900, and every few seconds hitting 1000. Normally, it sits right at 850/900 and purrs like a kitten. 5 min later it sputtered a few times, just as I was parking in the driveway. That's why I've been suspecting the heat soak/vapor lock issue, it's just been so unpredictable about it. Supposedly it's more our an issue on warmer days, and that hasn't seemed to have been the case.


-alopeks
Click to expand...


Thumbs up for thorough and complete check of the basics. The additional info on the symptoms makes me suspect a faulty Idle Air Controller. Heat soak/vapor lock typically occurs only with a hot engine start. I have had almost the exact same symptoms and determined it was a faulty IAC. The symptoms would come and go mostly randomly a few days or even a few weeks between occurrences. I didn't have any time to mess with it so I threw in a spare used IAC. The symptoms were cured for about a year, then they returned. With the prior experience, I purchased a new genuine Jeep IAC and the symptoms have not occurred again.
 
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