• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Weird idle/bogging out

X

xj1999sport

NAXJA Forum User
Location
Palmdale CA
Okay so i've been having this problem for a while now and i cannot figure it out. If i let my jeep sit for more than 15 minutes and then start it up it idles really low to almost zero rpm's but it will NOT die. If i start it up and take off it boggs really bad then it pops a few times from under the hood then i get a huge increase of power and its fine from there on out. If i start it and let it warm up for five minutes it runs fine with none of the above symptoms??? i'm seriously lost with this stupid problem, and yes i've searched and found nothing. i have replaced the throttle positoning sensor, idle air control valve, took apart the throttle body and cleaned it as well as i could, sea foamed the engine, replace the plugs, wires, cap and rotor and i have even cut the cat off to see if it was a clogged cat. Any help is appreciated. it's a 99 with the 4.0 and aw4
 
My first guess would be that one of the injectors is dribbling after it's shut off. This can be tested, but since it requires some specialized equipment you might do better to take it somewhere that already has that.

It occurs to me (edit here) that you might be able to do a preliminary check yourself if you produce the conditions under which it behaves badly, then crank the engine a couple of times with a remote starter switch (ignition/injection off). Now if you pull the plugs you can look for one that's wet.
 
TSB 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.

I know you said you have a '99, but the intake and exhaust manifolds are mostly the same, so I don't see why it couldn't be the problem. From what I've heard, the koozie solution offered by the stealership doesn't really do much. I pulled the whole fuel rail and wrapped it and all the injectors in heat sheath and cool tape. That seems to get it to happen less frequently. The next solution I'm working on right now is installing hood vents, after that I'm going to wire my electric fans (just ordered the kit from dirtbound) to stay on for awhile after shutoff.
 
sbrewster91 said:
TSB 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.

I know you said you have a '99, but the intake and exhaust manifolds are mostly the same, so I don't see why it couldn't be the problem. From what I've heard, the koozie solution offered by the stealership doesn't really do much. I pulled the whole fuel rail and wrapped it and all the injectors in heat sheath and cool tape. That seems to get it to happen less frequently. The next solution I'm working on right now is installing hood vents, after that I'm going to wire my electric fans (just ordered the kit from dirtbound) to stay on for awhile after shutoff.
Click to expand...


Based on the symtoms which are/were also the exact symtoms of my XJ I will have to agree with sbrewster91. After a hot start and I think I may have a problem, I let it idle for a bit before I take off. If I do take off imediately, I go easy on the gas to prevent the back fires through the intake.

In my XJ, it only happens on hot days in South Florida when I restart after 30 minutes or less. I do know it is very difficult to perdict with any kind of accuracy.
 
It hasn't been hot out here at all. It's been in the high 50's to mid 60's. The strange thing is, is that when I start it it's okay for maybe a minute at the most then it starts idling really rough and wants to die. I have no clue what could cause this..
 
I was having the same problem minus the low idle and bogging down at idle....When I would pull off at first...it would bog down and backfire through the intake....I changed out the rear 02 sensor and then realized that my heater circuit fuse was blown as well. Changed it out along with the rear 02 sensor and so far so good....
 
Matthew Currie said:
My first guess would be that one of the injectors is dribbling after it's shut off. This can be tested, but since it requires some specialized equipment you might do better to take it somewhere that already has that.
Click to expand...

quick check would be to pull the fuel rail and injectors from the intake as an assembly and arrange 6 glasses under the injectors. Pressurize the system and watch for leaks-- it would help if you could do this at full opperating temp. but it's not imperative.
 
easy test instead of taking the fuel rail off (not knocking it just start with simple then go to that) go to operating temp. hook fuel pressure gauge up to fuel rail fitting is inbetween the first and second injectors then let it sit for a little while. YES i know fuel pressure is supposed to drop over time but the system is supposed to hold 49psi for a good amount of time. If it does not hold the 49 psi get back to us
 
I have this as well, and I've been convinced it's heat soak....

I have a new header to put on, will it help if I coat or paint the header (NOT WRAP) ??
Will this actually reduce "under hood temps" and lessen my hot soak stumble ??
 
I also agree with replacing the O2 sensors i had the same symptoms and replaced all the same sensors and was at a loss. then i decided "hey changing the O2 sensors cant hurt since they have 160,000 miles on them." replaced the sensors and ran fine. the heater circuit on my upstream sensor was bad and must have caused the whole problem cause nothing else made a difference at all
 
wsar10 said:
I have this as well, and I've been convinced it's heat soak....

I have a new header to put on, will it help if I coat or paint the header (NOT WRAP) ??
Will this actually reduce "under hood temps" and lessen my hot soak stumble ??
Click to expand...


Ceramic coating may be the best solution to high under hood temperature.
 
You must log in or register to reply here.

Similar threads

P
interment problem
Replies
3
Views
2K
cruiser54
C
9
Renix lowish idle
Replies
10
Views
2K
90xj06
9
F
Stumped on this one!
2
Replies
29
Views
4K
Bent
Bent
V
High temp woes
2
Replies
21
Views
414
Vitzaa
V
A
Rough idle & CEL with no codes?
Replies
10
Views
3K
alopeks
A
Back
Top