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Unread 09-15-2009, 03:41 PM   #1
RDWhin01SS
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1999 WJ 
 
Join Date: Aug 2008
Location: IL
Posts: 4
4.0 stumble/surge off idle

Please help, this has been driving me crazy. I have a 99 wj with a 4.0 and it will stumble and stall when trying to idle. if given a little gas then let off it seems that it cant find where it should idle, but when it does it idles perfectly fine. It also has a hesitation when first accelerating, and occasionally when starting it cranks for a long time before starting. I have cleaned the throttle body and replaced the iac, tps, and map.

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Unread 09-15-2009, 05:33 PM   #2
4Slow9erHybrid
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1997 ZJ 
 
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Quote:
Originally Posted by RDWhin01SS View Post
Please help, this has been driving me crazy. I have a 99 wj with a 4.0 and it will stumble and stall when trying to idle. if given a little gas then let off it seems that it cant find where it should idle, but when it does it idles perfectly fine. It also has a hesitation when first accelerating, and occasionally when starting it cranks for a long time before starting. I have cleaned the throttle body and replaced the iac, tps, and map.
Does this stumbling happen shortly after starting the engine (2-3 mins) and lasts a short time 1-2mins. Most likely the upstream O2 sensor. You can diagnose this by disconnecting the O2 sensor for a few days (don't drive a 1000 mi like this). If the stubling symptoms disappear, you diagnosed a failing O2 sensor. Replace with original MOPAR only!
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Unread 09-15-2009, 05:44 PM   #3
RDWhin01SS
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thanks i will give it a try, yea it starts shortly after starting the engine and usually just occurs when coming to a stop or at very slow speeds where you are on the gas a little then back out of it... like in a drive thru, or traffic
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Unread 12-07-2009, 09:31 PM   #4
steveheibel
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1999 WJ 
 
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I was wondering if you ever found the fix for this
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Unread 12-07-2009, 11:11 PM   #5
StellaTheZJ
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This sounds a lot like a TPS issue. They are basically sliding switch, and they wear out in the region with most of the "sliding." The small section just off idle is rubbed every time you move off idle, and no other area is worn so much. This can be checked with a multimeter. Check your manual for the specs.
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Unread 12-08-2009, 02:49 AM   #6
RDWhin01SS
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i have yet to find a fix for this. the 02 sensors are both new, tps, iac, & map are fine, fuel pressure good, vaccuum is fine as well. has anyone else expierienced this and have more info?
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Unread 12-08-2009, 08:04 AM   #7
4Slow9erHybrid
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Quote:
Originally Posted by RDWhin01SS View Post
the 02 sensors are both new
what brand O2 sensors?
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1997 JGC Laredo 4.0 4x4 99900mi * 0W30 German Castrol since 75k * 225/75/R15 Firestone Destination AT on Ravine rims * winter 235/75/R15 Bridgestone Blizzak DM-V1 * UC suspension * Monroe Reflex Monotube shocks * factory skids * KOR steering brace * rear Addco SB * Magnaflow cat and cat back system * complete 5.9 interior
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Unread 06-20-2011, 12:12 PM   #8
fotonm
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After having this same problem on my 94 with a 5.2 I changed EVERYTHING that people have been talking about on here the TPS, New Tranny, New fuel filter, New fuel pressure regulator. Sometimes it would run great then other times just very sluggish and especially between about 1000 to the 2000 rpm mark. It didnt matter if it was hot or cold just very frustrating and intermittent.

Well I started to suspect a vacuum leak. While monkeying with the vacuum lines and wiggling them I got a surge and thought I was on to it. It wasn't the vacuum after all.

It was the wires that go into the TPS and when I would wiggle them it would surge and even cut off the engine. I unplugged it and Ohmed out the wires while my ohm meter was plugged into and wiggled the wires and I didnt get any Resistance drop. I figure out that the pin that comes out from the ground part of the TPS was not making a good contact with the connector. When it was not making a good solid contact I would get the problem.

You can fix this one of two ways.... you can replace the entire plug assembly to one where the female end of the connectors make a better contact or you can take up the slack in the now too loose female end with a small piece of wire inserted into the tooled out female end (lol) and now it wont be like a hotdog in a hallway and will make a good ground. Plugged it all back in and now runs like it should with full power all the way through the spectrum.

This worked for me so you may try this!! Its a connection and grounding problem not an actual prob with any of the devices.

if your grounding and connections in that TPS are not solid it spikes all up and down sending the wrong voltage to the rest of the injection system.
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Unread 04-18-2013, 04:08 PM   #9
Christianofojai
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2000 WJ 
 
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Location: Ojai, Ca
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I’m having the same problem. It’s been driving me crazy. I noticed this problem with mine is intermittent and when it happens it’s also acompined by the smell of gas out of the tail pipe. I thought O2 sensor butt after replacing them all it still does it.
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