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Unread 09-27-2007, 07:54 PM   #1
chim
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1995 YJ Wrangler 
 
Join Date: Mar 2006
Location: Near Lancaster PA
Posts: 218
Runs real rough (when cold only)

My 95 4-banger (MPI) runs very rough until the engine comes up to the point that the thermostat opens, then it runs perfectly.

Until the engine gets heated up, it runs rough and stalls very easily. Most times it will keep running at a stop sign. Unless I carefully "play" the throttle to get the revs up a bit, it stalls out when I try to pull away.

When I accelerate it begins to miss badly when the revs get to about where I shift.

Strange thing is that after the stat opens, it runs like a Swiss watch - it will let me pull out from a stop with the engine at idle speed, and there's not even a hint of a misfire.

I removed and cleaned the throttle body and replaced the idle air control valve actuator, but it didn't help. Any ideas? Thanks..............chim

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Unread 09-27-2007, 08:31 PM   #2
Jeepinjon
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1995 YJ Wrangler 
 
Join Date: Oct 2005
Location: Bellwood, Pa
Posts: 315
Have you swapped out the thermostat? You keep mentioning it...why not try that?
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Unread 09-27-2007, 09:16 PM   #3
Brown Dog
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1991 YJ Wrangler 
 
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Location: Queen Creek, Arizona
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Have you checked the codes? Not all codes illuminate the check engine light.

I am thinking that MAP sensor, and/or TPS (a faulty TPS does light the check engine light).
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Unread 09-28-2007, 08:14 AM   #4
chim
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1995 YJ Wrangler 
 
Join Date: Mar 2006
Location: Near Lancaster PA
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Thanks, that will give me something to check. The stat was replaced ~ 2000 miles ago.

I mentioned it because the engine changes the way it runs at the point that the stat opens. You can see the temp gage peak and then drop off a few degrees. At that point, the engine runs smooth.................chim
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Unread 02-20-2012, 03:38 PM   #5
Tre3
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1997 ZJ 
 
Join Date: Dec 2011
Location: Elk River, MN
Posts: 100
i have the same exact problem, i just cleaned the throttle body 2 days ago and it didn't change anything, and im starting to get worried with how easily it seems to almost stall. did you find out the problem or does anyone know if its related to the transmission? only happens it the cold i noitced it started at about 40 degrees or colder. ( just bought the jeep last summer so i dont know whats all been replaced)
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Unread 02-20-2012, 03:45 PM   #6
MaddBones702
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1989 YJ Wrangler 
 
Join Date: Jun 2011
Location: Henderson, NV
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If you have a cto valve that would be worth verifying that the lines are all connected beginning to end.
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Unread 02-20-2012, 04:05 PM   #7
Tre3
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were would it be located? and how would i check to make sure everything is working? sorry im still new to trying to work on it
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Unread 02-20-2012, 04:54 PM   #8
Tre3
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on a side note im leaking transmission coolant i was told, could that be any connection?
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Unread 02-20-2012, 07:19 PM   #9
oldtime_ironman
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1991 YJ Wrangler 
 
Join Date: Dec 2010
Location: 14304 Niagara Falls, NY
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None of the above make much sense to me. When its cold the engine runs on the coolant temp sensor and the TPS, not much else. When it switches into closed loop, then it listens to the O2 sensor and all the other stuff. Closed loop happens somewhere around 185 deg F. So I would test the coolant temp sensor and maybe the wiring to/from that first. Its the temp sensor in the thermostat housing - since you replaced the t-stat, I would double check the wiring and connections to that sensor first. If thats OK, then the sensor itself should read about 185 ohms at 210 F.

Hope that makes sense and helps!
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Unread 02-20-2012, 09:13 PM   #10
ParkerJ
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1991 YJ Wrangler 
 
Join Date: Jan 2012
Location: Pittsburgh, PA
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I had the identical issue, its your crankposition sensor. Mine would run awful till it warmed up but eventually it got to the point that even when warmed up it missed, idled crazy and stalled. I replaced almost all the sensors, cleaned the throttle body and even changed the ignition coil...but after all those attempts to fix it came out to be the crank position sensor. Trust me on this, I just went through this. Good Luck
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