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Unread 08-15-2013, 05:35 AM   #1
JaneLee
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1994 ZJ 
 
Join Date: Aug 2013
Location: Richmond, IN
Posts: 35
stumbling idle after warmed up

i have a 94 grand cherokee laredo 4x4. i am pretty mechanically inclined but i'm at a loss on this one. there were no problems starting and idling fine, then starts stumbling during idle after it warms up. drops maybe 200 rpm after put into gear and sounds like it wants to stall at complete stop or slow down. i replaced spark plugs, and wires maybe a month ago. i dont see or hear and vacuum leaks, idle air control looks fine, not gummed up, cat converter has no rattle. ran fine until i replaced the water pump now having issues. someone help

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Unread 08-15-2013, 10:43 AM   #2
Oldfrog
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1997 ZJ 
 
Join Date: Feb 2008
Location: Louisiana/Texas
Posts: 4,045
The upstream o2 sensor is taken into the loop after warm up, as I understand it. Based on that info, I'd disconnect the plug on the upstream o2 sensor and try it. It will throw a code, but if it cures the problem, you can replace the sensor with an NTK brand sensor. ( dont use anything else).
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Unread 08-15-2013, 02:12 PM   #3
JaneLee
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1994 ZJ 
 
Join Date: Aug 2013
Location: Richmond, IN
Posts: 35
ok tried that. it did throw codes but did not improve the running. was worse. any more suggestions?

edit: electrical connections look fine and clean. replaced tb gasket, was missing lol no access to scanner due to it being a 94 no one in town has one, of course just my luck
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Unread 08-15-2013, 03:15 PM   #4
PolkaPower
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1998 ZJ 
 
Join Date: Aug 2011
Location: The Abyss, MD
Posts: 16,237
Sounds like an 02 problem. The Jeep runs off pre programmed settings until it's warmed up then it takes info from the 02. If you want the trouble codes, cycle the key on and of 3 times and the check engine light will blink on and off. Two blinks fast together indicate 2 numbers, one blink then pause indicates single digit. 12 and 55 don't count.


There is only one 02 on 93-95 ZJ's.
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Unread 08-15-2013, 05:30 PM   #5
JaneLee
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1994 ZJ 
 
Join Date: Aug 2013
Location: Richmond, IN
Posts: 35
yep. there is only one o2 sensor. unplugged it and there was no running difference but it did give me the codes 12-27-55. no single digits, or singles listed in the repair manual i have. oddly enough i did think to unplug the MAP sensor. i was told that i should notice a difference, probably would run worse. i unplugged it and the jeep started running perfect in P. when i put it into gear it bogged down and died which i was told should not happen. All this was done while the engine was warm so know i dunno.
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Unread 08-15-2013, 05:32 PM   #6
PolkaPower
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1998 ZJ 
 
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Location: The Abyss, MD
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Look for the trouble codes. This tell you that it may be an injector problem. http://www.nagca.com/grandtech/troubleshootcodes.htm

http://www.naxja.org/forum/archive/i...p/t-57327.html
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Unread 08-15-2013, 05:41 PM   #7
JaneLee
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1994 ZJ 
 
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Location: Richmond, IN
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right from code 27 but 27 is a listing in the repair manual for every injector. it cant be all of em can it?
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Unread 08-15-2013, 05:59 PM   #8
PolkaPower
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1998 ZJ 
 
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No probably not. I was wondering since the MAP sensor controls AF mix if that was what tripped the code.
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Unread 08-15-2013, 06:04 PM   #9
JaneLee
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1994 ZJ 
 
Join Date: Aug 2013
Location: Richmond, IN
Posts: 35
i dunno if that was the cause since if i put it into any gear and tried to drive it at all it would sputter, try to die and backfire. i know this combined with getting hotter than usual from the water pump going out can push an old MAP sensor into going bad too. would stay running though very rough if i left it in P or N but i know that's because there is no strain on the engine too
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Unread 08-15-2013, 06:08 PM   #10
PolkaPower
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1998 ZJ 
 
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Location: The Abyss, MD
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Sp there are other things wrong with the Jeep too? You should fix all known issues.
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Unread 08-15-2013, 06:13 PM   #11
JaneLee
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1994 ZJ 
 
Join Date: Aug 2013
Location: Richmond, IN
Posts: 35
before the water pump went bad it had no issues i noticed. i replaced it and started having this problem with it being driveable and running bad. it seems to be getting worse. the first actual problem i found was the odd that changed the bad running at all was when i unplugged the MAP sensor and the rpms ran normal in p and n but it dies if you put into any gear
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Unread 08-15-2013, 06:14 PM   #12
dusterdude
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1996 ZJ 
 
Join Date: Jan 2012
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I was told long ago,if you unplug the map and it runs like it should,the map is bad but do not run it very long unplugged
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Unread 08-15-2013, 06:30 PM   #13
JaneLee
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1994 ZJ 
 
Join Date: Aug 2013
Location: Richmond, IN
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right. i was also told long ago not to let it run long unplugged. i will replace the MAP sensor tomorrow and see if that fixes the problem. i will definitely let y'all know if it works
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Unread 08-15-2013, 11:26 PM   #14
jabba974
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1996 ZJ 
 
Join Date: Mar 2013
Location: Ionia, MI
Posts: 246
My thought is that its a fuel issue....When its cold, the engine idles higher, which requires more fuel... as it warms, it idles down, less fuel....I would replace the IAC sensor before the MAP....I could be wrong, but I always thought the MAP had to do with acceleration....I dont believe that all of the injectors would go bad at once...maybe 1 or 2...but def not all of them....easy to tell if they are working...use a mechanics stethoscope to listen to them pulse...
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Unread 08-16-2013, 04:08 AM   #15
JaneLee
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1994 ZJ 
 
Join Date: Aug 2013
Location: Richmond, IN
Posts: 35
the IAC was one of the first things i checked, it seems to be working fine, though someone just told me that the I6 are notorious for eating the o rings on them so i'm gonna check that out too. i also checked the fuel pump pressure which was ok (33psi). as far as i can hear all the injectors seem to be working, i even double checked the spark plugs and wires i installed in case i got a bad one out of the bunch
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