hot day..engine runs bad

Ok here we go..
98 xj 4.0.
on hot days the yellow engine light comes after driving a while.
The yellow engine light comes on. It idles really rough and sometimes stops completely and is difficult to start.
This has been happening for a couple of summers and never happens on short trips or in cooler weather.
I replaced the flywheel sensor on the bell housing last year because folks told me they tend to malfunction when they are older and hot but the problem is back this year.
The yellow engine light may stay on a couple of minites or even days but it always eventually goes off and I never have a problem at all in the fall, winter, or spring.

Any ideas?


Kepp the Durty side down,


Joe Durt

I'm assuming by "yellow engine light" you're talking about the check engine light....

Option A, get near an Autozone when you know it's going to act up and the light comes on. They will read the codes for free for you, and from what the symptoms you describe, once you get the code you'll have a pretty good idea of where to begin with repairs.

Option B, which I would recomend even more than option A, is to invest in a OBD-II scanner of your own (IMO, a must have for the DIY mechanic with any 1996 or newer vehicle) and have it ready to go when the Jeep starts to throw a fit. If you were to invest in a scanner (they can be had for well under $100), it would pretty much pay for itself the first couple of times you need to read a code.

Also, do you have the full gauge cluster (Includes engine temp, oil pressure, voltage gauges, in addition to a tach), or dummy lights? If it's the full gauge, how is your engine temp when it begins to spaz out?

My 2000 Sport has been doing something similar on hot days, but only when I first start the engine while it is hot. Usually it is after I have been in traffic with the AC on and the engine is a little hotter than normal. Then when I try to restart it after setting for a few minutes, it will idle rough with almost no response to the throttle. After a minute or so, it smooths out. The CEL came on recently when this happened but cleared a few hours later. I have almost 180,000 miles on mine and that is the first CEL that I have had.

What I do now when the engine is hot is give it a small tap on the throttle as I start it. Seems like the extra RPMs gets it over the rough idle and it smooths out quickly.

00xjsebb said:

My 2000 Sport has been doing something similar on hot days, but only when I first start the engine while it is hot. Usually it is after I have been in traffic with the AC on and the engine is a little hotter than normal. Then when I try to restart it after setting for a few minutes, it will idle rough with almost no response to the throttle. After a minute or so, it smooths out. The CEL came on recently when this happened but cleared a few hours later. I have almost 180,000 miles on mine and that is the first CEL that I have had.

What I do now when the engine is hot is give it a small tap on the throttle as I start it. Seems like the extra RPMs gets it over the rough idle and it smooths out quickly.

Click to expand...

My 2001 does the exact same thing. Buggs the piss out of me:flamemad: :flamemad:

Yall's problem is what is referred to as "heat soak." Basically, due to a fault that chrysler admitted to, the fuel is evaporating before it has a chance to make it though the injector (dont recall which one off the top of my head is most prone to it), and untill the computer can compensate for the fuel loss, it misses and runs like crap for a minute or so.

There was a recall I believe for this problem on the 2000's....and I believe the 2001's....basically it involves wrapping the injectors with insulation to help keep some of the excess heat out.

Search more on here for "heat soak" and you'll find more on what i'm talking about.

The CEL is more than likely coming on and throwing a code for a "cylinder misfire"....which makes logical sense, given whats happening

if you have a silver foil looking thing on the top of your intake manifold, then i believe that was the "fix" from chrysler for the fuel vaporizing problem....

I've got the silver foil shield on the intake manifold, though I thought it was a fix to prevent engine fires due to accumulated debris in that area. The stumbling idle does act like heat soak, but my Jeep only started experiencing this after about 150,000 miles. The injectors do not have anything wrapped around them, so they may be getting hot. Maybe the injectors are not sealing as good as they used to allowing the heat soak to finally become a factor.

One thing I did that seemed to help was run a large bottle of Valvoline injector cleaner through it. It has started and idled normal everytime for the past couple of weeks.