Odd rough running engine today

So I made a trail run today with my XJ. This is pretty much the first trail run it's made since I've had it. We stopped for about 6-8 minutes at one point and I parked on a pretty decent uphill against the bank of a hill, front end up. We went to leave and all of the sudden when I started it up it was idling terribly. Real rough, almost like a plugged exhaust or intake. Throttle applied and it would bog slightly but then would gain momentum. Once the rpms came up it seemed to smooth out.

So I decided to move on and give it a go. It seemed to smooth out quickly once going. It didn't seem to be down on power once rolling in 4lo. We stopped once more a short way down the trail and I was more level. It had the same symptoms, but much less severe. From there on it seemed fine. I stopped to air up at the trailhead and I drove 40 miles home with no signs of the problem again.

Any ideas WTF that was? I've only owned the truck for about 5 months and have never had any issues with the engine.

I have no idea what causes this but I did want to let you know I have the same problem. It doesn't happen very often but usually I will drive about 35 mins away, leave the jeep for about 20 mins and when I start it up it has that terrible idle. After it sits for a min or two it calms back down but I find it very strange. It happens on the trail like yours does also.

Look up heat soak on naxja. Thats the cause of your issue. You just need to let it sit for longer or leave it running. I don't think it hurts anything when it does it but it is irritating. Mine does it too. It happens in the late model XJ's.

Interesting. I've never had the problem before and it was maybe 55° outside yesterday. I'll have to keep an eye on it and see if I can minimize it while wheeling.

It does sound like the heat soak issue. What year is your XJ?

Meant to mention that... it's an '01. Engine temp looked fine all afternoon at 210° and below/

Yeah there was/is a bulletin or recall on that issue. Its not an engine temp issue. It has to do with one or more of the fuel injectors becoming "heat soaked" do to the design of the newer style intake manifold I think. The fix involves insulating the injectors. Do a search, there is a lot of info on this problem.

I had the same problem, here's the TSB as someone gave it to me...

NUMBER: 18-031-03
SUBJECT:
4.0L Rough Engine Idle After Restart Following A Hot Soak
OVERVIEW:
This bulletin involves the installation of a fuel injector insulator sleeve.
MODELS:
2000-2004 (TJ) Wrangler (Domestic and International Markets)
1999-2004 (WJ) Grand Cherokee (Domestic and International Markets)
2001-2004 (WG) Grand Cherokee (International Market)
2000-2001 (XJ) Jeep Cherokee (Domestic and International Markets)
NOTE: This bulletin applies to vehicles equipped with a 4.0L engine (sales code = ERH)
SYMPTOM/CONDITION:
Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked
engine. This condition may be most noticeable when the engine is restarted following a
prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90ºF)
or higher. This condition may be consistent with short city stop-and-go driving trips and
can be aggravated by the use of fuel with a high ethanol content. Depending upon
various conditions a MIL may occur due to DTC P0303 - Cylinder #3 Misfire.
This condition may be caused by heat from the exhaust manifold that following engine
shut down migrates to the area around injector #3 and causes fuel vapor to form
within the injector. This in turn may cause a momentary misfire of cylinder #3 until
the fuel vapor is cleared of injector #3. The insulator sleeve lowers the injector #3
temperature to a point below which the fuel will not normally vaporize.


NOTES: the injector koozie from the dealer is crap, never got it myself. I'm currently testing a "wrap it in heat tape" solution, not sure if it's helped yet. and despite what the TSB says, it happens if its warm out at all, not just above 90º.

00 and 01 4.0s are the most susceptible to "heat soak". Very common.

Jeep TSB fix is lame. I put it on my 99 and although I don't have a serious problem with heat soak, the injector insulation didn't make any difference.

Other options are hood louvers and an e-fan timer which leave the fan on for a programmed period of time after you turn the engine off to reduce engine bay temps. The timer has had pretty good success from what I've read..........

SEARCH for the above terms and you'll find more than a few posts.