Stumble/hesitation and bad idle

[Minty]

Hey guys, just bought this 96 XJ, and it's having a hell of a time idling, and driving. All is good for the first few minutes, then as I'm just cruising along it will start to buck, jump, and stumble. It always seems to be right around 1500 RPM +/- 200. When it starts to hesitate, I can mash the throttle and after some jumping and sputtering it will get past it's "dead spot" and act pretty good above ~2000 RPM. Then when I push in the clutch, RPM will drop down and ALMOST die, but keep itself going.

Previous owner claimed it needed a new IAC valve, and when I test drove it, it only sputtered a couple times and not as bad as it is now.

I compared the IAC valve to a new one, and the pintle wouldn't turn on the "bad" one so I replaced that. Also tossed on a new TPS, and fuel filter, and cleaned out the throttle body, which was really dirty. Added some fuel system cleaner, although it probably hasn't ran long enough for it to do much. Also, did some looking for vac. leaks, sprayed carb cleaner around but all hoses look good and no spikes in idle.

Any ideas on where to go from here? :bang: CPS, MAP...?

[4.3LXJ]

What does the temp gauge say when it starts to have problems. In other words, does it happen when it is almost warmed up?

[Minty]

From what I can tell, it seems to get worse the longer I drive it. It always fools me, I'll do something to it and take it out for a test where it acts great at first and then a little sputter, and then before I know it I'm limping it back home. So yes, I would say the hotter it is the worse it gets, what does that point towards?

[4.3LXJ]

From what I can tell, it seems to get worse the longer I drive it. It always fools me, I'll do something to it and take it out for a test where it acts great at first and then a little sputter, and then before I know it I'm limping it back home. So yes, I would say the hotter it is the worse it gets, what does that point towards?

O2 sensor i think. It is probably running too lean. When was the last time it was changed?

[nickxj94]

Still have the catalyst converter? My buddy's 97 had a similar issues with idle and running he cut it off its ran alot better now he just has to buy a new one lol! May check that out too

[Minty]

O2 sensor i think. It is probably running too lean. When was the last time it was changed?
O2 sensor sounds like a good option! Previous owner said he did all the normal tune-up things, but never said anything about the o2 sensor so that very well could be it.


Still have the catalyst converter? My buddy's 97 had a similar issues with idle and running he cut it off its ran alot better now he just has to buy a new one lol! May check that out too
As for the exhaust, it doesn't have a cat or a rear o2 sensor, is this affecting it at all? I was reading it's ok to run without a downstream o2?

[4.3LXJ]

At the very least, you should have a check engine light. It might be nice to take to an Autozone and get the codes read and see what they are.

[Minty]

I will get it down there tonight to get it read, I'm sure there are codes on it by the way it's running but I think the light is out of the CEL... We'll see what it pulls up.

[4.3LXJ]

OK, that will tell us more

[XJ Wheeler]

Might check the fuel pressure too.

[Minty]

4.3LXJ... you are my hero. You are 2 for 2 with me already haha! Also thanks to the others who had suggestions!

Went down to AZ for the scan, came back with 3 O2 codes! (I guess my CEL bulb is out...) Pulled my sensor out, and it definitely looked old and worn. Tossed the new one in and took it for a spin to get it up to temp. with zero issues. Glad to say this issue is solved, thanks boys!

[Brasscatz]

Glad to hear it! We're pretty proud to Steve on here.... hope he never leaves!