Help! Rough idle and "sputtering"

[cherokee4x4]

When my jeep is at idle in park, it is idle-ing very rough. When I go to put it in drive and accelerate, it hesitates and the rmp's bounce around and jolts me forward and back, unless I step on it hard. I replaced plugs, wires, cap and rotor and also cleaned the IAC, and still seem to be having issues:bang:. Gas mileage also seems to be worse than usual. Can anyone tell me what needs to be fixed/replaced?

[4.3LXJ]

You didn't say if you had a check engine light, but I suspect you don't. I also suspect you have not changed your O2 sensor in some time, if at all. I think your fuel/air mixture is too lean caused by a worn out O2 sensor. The telltale thing I see here is that when you mash the skinny pedal, it straightens out. When you do that the PCM will make the mixture a little richer which would allow it to run right

[cherokee4x4]

Yea sorry I forgot to mention no check engine light. I recently replaced the downstream O2 sensor but not the upstream. Maybe that's what's next then. I'll let you know if that fixes the issue. Thanks!

[cherokee4x4]

After struggling to remove the O2 sensor for the last couple days (it was very stuck, and looks like factory, and my jeep has 178000miles.........) and installing a new one, the problem is still there. Started it up, ran fine for a minute as usual, then began to jump around in Rpm's.... :bang: talk about a PITA

[prcjeep]

I don't see it previously mentioned, but the first thing i would check/replace if my xj was doing this is the TPS, throttle position sensor. 30-35 bucks at most auto part stores with lifetime replacement warranty. (I always carry a spare in my glove box)

[cherokee4x4]

Ok that will be next after I get back in town after this weekend. Someone else said possibly a bad manifold and manifold gasket? My jeep does have an exhaust tick so this could also be the culprit. But then TPS is obviously cheaper. I just hate throwing money at guesses

[4.3LXJ]

Ah, exhaust tick. Glad you mentioned that. A manifold leak can suck air into the system and make the O2 sensor read lean. How are your plugs?

[prcjeep]

Ah, exhaust tick. Glad you mentioned that. A manifold leak can suck air into the system and make the O2 sensor read lean. How are your plugs?

suppose that could make it fail emissions tests too??

[cherokee4x4]

Just replaced the plugs a couple days ago. Ones I took out where actually not to bad, but they were Bosch so they are trash no matter what.

[4.3LXJ]

suppose that could make it fail emissions tests too??

Yes it can. Not always, but sometimes

[cherokee4x4]

ok so I just finished replacing the TPS as mentioned, and still no change.. :mad0090:

so far its been new plugs, new cap, new rotor, new wires, cleaned IAC, new TPS, new O2 sensors. I'm not sure what to do next.

[4.3LXJ]

Does it idle well at any time?

[cherokee4x4]

Yes it idles fine after it has its "fits". Every time I start it up after its been sitting for a little bit, it has somewhat of a difficult start(sometimes it starts just fine) and after a little bit of running, it begins to idle very poorly. After I put it in drive and start going, it's hesitates and "bucks" for about 10 seconds and then it goes back to normal. Then it's fine until I shut it off.

[4.3LXJ]

Checked your crank position sensor lately?

[cherokee4x4]

just ordered one for cheap. Hopefully that'll do the trick cause im wasting all my money on this "heep" ;):D

[4.3LXJ]

I hope so too. The CPS can give intermittent symptoms like that. The type of thing you have can be very difficult to nail down. Make sure the connection is good too. Sometimes that can do what you are describing also. You might also check your fuel pressure too

[cherokee4x4]

ok so today i was reading through a forum not even closely related to this issue and someone mentioned something about an O2 sensor fuse... According to them it is a "little known fact" that xj's have one of these. I tracked down said fuse and sure enough it was blown and broken. I had a fuse handy, replaced it, started the jeep, and sure enough, no signs of extreme rough idle or bogging down when driving. Still has a slight rough idle though(moves between 700-900) which it has always had, but i can deal with that. Im pretty sure that my issue is fixed for now, but if that changes, i will keep you all updated. Thanks for your help. Hopefully this can help someone else with the same issue. :)