I recently ran into an odd situation with my '98 Cherokee XJ 4.0. It started when the wires to the oxygen sensor aft of the catalytic convertor worked their way down to the driveline and were damaged. Shortly after, the CEL came on and the problem started. After sitting overnight or several hours, the engine will start fine and idle smoothly. Within 3 to 5 minutes after the start-up it will start idling rough...almost loping. It will do this for about 5 seconds, then the rpm's will jump up, settle down, then run smoothly again. There will be no other issues throughout my trip. I had the codes checked with a reader and it showed both O2 sensors as bad. I replaced the downstream sensor which had the damaged wires...still had the rough idle. I then replaced the upstream sensor...still have the rough idle. Now I am getting the CEL again. Checked it with a reader and it is now showing the upstream O2 as bad again. I did a cold start start today and watched the engine for anything unusual. After about 5 minutes of running it started running very rough. The only thing unusual that I noticed was that there was a great difference in air that was being pulled through the air intake filter box after the rough idle started....it sounded like a tornado inside there. I am also seeing an unusual amount of moisture/water from the exhaust pipe. This may just be everything heating up in 30 degree weather, but I didn't really notice it before the rough idle problem. Any suggestions as to what my problem could be or what to look for would be greatly appreciated.

 

Have you inspect the wires leading to the 02 sensor?what sounds to me that is going on is,after 2-4 minutes your 02 sensor heats up and goes into closed loop at idle,not cruise until you reach normal operating temp,when it goes into closed loop the pcm starts to use input from the 02 sensors,if there is a torn wire that you have missed the pcm will not know what to do,it works with what it has.
fyi,an engine mis will cause the 02 sensor to throw a code,all it has to see is a lean or rich mixture that will put it out of its range,0.04-0.95 volts approx and the 02 sensor will say I am bad,it is followed by other codes also,if those components are bad,but not always.
Also your jeep was fine up to this point correct? then it most likley has to do with ripping these wires out.

 

Thanks for the info, Abovetimberline. Yes, up to this point there were no problems. The wires that were damaged were between the sensor and the main harness. The new sensor came with and replaced the wires that were damaged. It's kind of hard to explain how the damaged occured, but the insulation was just ground off. It never really ripped them out to the point where the main harness would have been damaged. Is it possible that when these wires were damaged that other sensors such as the IAS or TPS could have been damaged? Also, after replacing these O2 sensors, will the computer have to re-learn?

I just came in from doing a cold start and was editing my original post when you replied. Here is what happened...

I did a cold start start today and watched the engine for anything unusual. After about 5 minutes of running it started running very rough. The only thing unusual that I noticed was that there was a great difference in air that was being pulled through the air intake filter box after the rough idle started....it sounded like a tornado inside there. I am also seeing an unusual amount of moisture/water from the exhaust pipe. This may just be everything heating up in 30 degree weather, but I didn't really notice it before the rough idle problem.

 

Did you ever get this sorted? If so what was the problem?

Mine does ths too, exactly like this.


A little history. when I bought it, it had a code for O2 sensor, I replaced it and it came back, so then I thought I had an exhaust leak and I have just replaced the header. The code has not come back (yet), but it still runs rough exactly like you described, there must be something in common, it is too coincidental, any update?

 

Gintaras, What happened on mine was the O2 sensor wire grounded out on my drive line and blew a fuse in the fuse box. I replaced both the O2 sensors and still had the same problem. A fellow on this forum told me how to fix it. I replaced a fuse and it never did it again. It is an unmarked fuse. I just went out and checked; it is a 15 amp on the first row second from the bottom if you are looking at the box from the side. Let me know if that fixes it.

 

Thanks, but since I changed the manifold, i have not seen the O2 code come back but now I have a cyl 1 misfire code that i need to address.. it still idles rough, but now it is a different code.

 

my jeep is doing almost the same thing but no check engine light has come on and it idles rough right at the start up then smooths out after about 5 minutes. sounds like a tornado in my air intake as well and i have moisture coming out of my tail pipe. it just started after i replaced my lower radiator hose which i cant understand why that would effect anything. any suggestions?

 

Did you have the same problem with oxygen sensors? I might say check the spark plugs, but I'm not sure. Let me know if you get it figured out.

 

it did it one day and i came and wrote the post, hasnt dont it again since then, today was a good day, accept now i have a little white smoke after cold start up

 

mine has the same issue im gonna check the fuse your talking about and see if its bad thanks for posting the fix for your prob

 

I recently ran into an odd situation with my '98 Cherokee XJ 4.0. It started when the wires to the oxygen sensor aft of the catalytic convertor worked their way down to the driveline and were damaged. Shortly after, the CEL came on and the problem started. After sitting overnight or several hours, the engine will start fine and idle smoothly. Within 3 to 5 minutes after the start-up it will start idling rough...almost loping. It will do this for about 5 seconds, then the rpm's will jump up, settle down, then run smoothly again. There will be no other issues throughout my trip. I had the codes checked with a reader and it showed both O2 sensors as bad. I replaced the downstream sensor which had the damaged wires...still had the rough idle. I then replaced the upstream sensor...still have the rough idle. Now I am getting the CEL again. Checked it with a reader and it is now showing the upstream O2 as bad again. I did a cold start start today and watched the engine for anything unusual. After about 5 minutes of running it started running very rough.



I had the exact same thing happen on my 99.It was rubbing on the driveshaft and it ground down the wires to the oxygen sensor.I replaced both of them and after a day or two it will keep throwing the oxygen sensor codes.I checked all the fuses and they are all good.What else could be wrong?

 

I figured it out it was the damn fuse.I finally noticed it was burnt after the third time checking it..I changed both sensors cleaned my throttle body and was basically pissed off for a few days.But everything is good now no codes.

 

my idle problem on my 99 xj was caused by the pre-cat O2 sensor. i replaced it with a factory direct sensor per suggestion of my mechanic, this was due to the fact that aftermarket sensors dont always send info as fast as the computer wants to recieve it, mine would not cause a check engine light either, ive been rough idle free for 3 weeks now. hope this helps