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Jeep Stumbles at Idle, runs rich

J

jeepster_259

NAXJA Forum User
Location
West Palm Beach, FL
I went out and bought a new o2 sensor ($70 later) since my jeep had been stumbling at idle and running really rich. When the o2 sensor is unplugged, it runs fine. Anyway, I plugged it in and the jeep ran great, nice and smooth, better power and shifting, CEL is out after resetting computer.
After a 20 min. drive, CEL comes on and it starts doing the stumbling at idle and running really rich again. I can smell gas while I'm driving and carbon comes out of the tailpipe pretty heavily.

So, now it appears that my old o2 sensor might not be bad. When i pull the codes it's saying o2 heater and misfire. If I unplug the O2 sensor, the codes stay, but the jeep runs fine.

Any suggestions??? I'm about to go on a 4 hour road trip to go wheeling and would like to figure this out.
 
Isn't the O2 heater circuit fused, possibly at the relay/fuse box under the hood? I'd check that out and also closely inspect your O2 circuit wiring for damage.
 
I've checked all my fuses and they are good, along with relays. Does anyone know which specific fuses/relays are for the o2 sensor/heaters?

Also, one thing I didn't mention in the first post is that it runs smooths while driving, no stumbling, but still runs very rich. It just stumbles at idle.
 
Yes. The only that I can imaging about what is making an engine running rich;
a bad CTS (Coolant Temp Sensor) and a bad MAT (Manifold Air Temp Sensor).
Sorry I am out of any further ideas at this moment, I hope it was helpfull. :shhh:
 
Last edited:
I might try replacing those. the thing that boggles me is that when the upstream o2 sensor is unplugged it runs fine. Only when it's plugged in is there a problem, which leads me to believe it has to do with the o2 sensors. However, after having put in a brand new o2 sensor and having the same problem, I'm stumped!
 
I guess that's next. It's just so damn expensive to do that.

I even went through and replaced every fuse and relay last night even though none were blown/malfunctioning. Tried banging on the cat to see if it was plugged, no change.

This sure is frustrating.
 
Perhaps someone knows better than me about this, but would unplugging the battery and resetting the ECU be necessary when changing the sensors? This would force the ECU to relearn.
 
i'm haveing the same problem with my 98 but it's not to the point where it worries me that much considering the other engine toubles i just got through.

because of them engine problems i mentioned i replaced almost every sensor under my hood except my o2 sensors and the IAC(idle air controler) because i didn't think they could cause the drastic problems i was haveing so even with all those new sensors (it turned out to be a bad ground) i still have the same problem i'm planning on putting 2 new 02 sensors with this paycheck and i'm gonna try swaping out a sapare IAC i have from the JY and see if that clears anything up.

let me know if u figure anyhting out because my gas mileage has taken a pretty good dive with this whole problem
 
alright, well at I'm glad to finally find out I'm not alone in this problem.

I've tried replacing IAC, CTS, MAP, and TPS, all with no change. New upstream o2 did nothing.

I think in the next couple of weeks, I'm going to try replacing both o2 sensors and the cat and muffler (I know my cat and muffler are on their way out anyway). Even though that's a good chunk of change, I'm hoping it will finally fix things.

let me know if you find any fixes as well!
 
yeah i'm kinda leaning towards downstreme o2 sensor because i had trouble with it when i bought my jeep and i put in a used on off of my parts jeep, because i didn't have the cash for a brand new one, and it corrected the problem for a while but now it's back so i think i'm gonna have to spring for a new one because i can't afford how fast my gas has been going.
 
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