1998 jeep grand cherokee laredo 4.0 idle problem - Page 2 - JeepForum.com
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Go Back JeepForum.com > Models > Jeep Grand Cherokee & Commander Forums > ZJ Grand Cherokee Forum > 1998 jeep grand cherokee laredo 4.0 idle problem

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Unread 07-18-2013, 11:59 AM   #16
hardbodyjeep
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Join Date: Jul 2013
Location: rockledge, fl
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Ok had battery tested it was fine injectors seem to be fine but while I was triple checking for bad hoses I found 2 one inch long hoses that are on a really tiny tube that leads back into the gas tank near the fuel pump idk what its for but both the hoses were cracked and rotted on my way to get some new hoses now and should have them back on in like an hour ill post back and let everyone know if this helps

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Unread 07-18-2013, 01:04 PM   #17
dellis
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1998 ZJ 
 
Join Date: Feb 2013
Location: Vienna, VA
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Those are part of the EVAP system, and is very likely a vacuum leak causing problems. But, I thought failure of that system was supposed to throw all sorts of codes ...
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Unread 07-18-2013, 01:18 PM   #18
hardbodyjeep
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Man this is deff a problem I'm tracking down this line and I'm find tons of places where it isn't even connected I have to take out the driver side headlight soo its gonna take a little bit longer then I expected ill post back soon
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Unread 07-18-2013, 03:56 PM   #19
hardbodyjeep
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Ok finally done the idle is not as rough and the idle fluctuation cleared up by prob 25 rpm at idle now it stays at 500 rpm and fluctuates to about 425 isn't 500 pretty low I thought they were suppose to idle around 600-650? But idk ill probably just do 2 new o2 sensors and tps sensor and if that doesn't work call it quits cause idk what else to do
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Unread 07-18-2013, 04:33 PM   #20
dellis
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My '98 4.0 idles with oscillation in the 710 to 730 range.
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Unread 07-18-2013, 05:56 PM   #21
NewtoZJ
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1998 ZJ 
 
Join Date: May 2012
Location: Columbus, Ohio
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Mine has the same surges and drops in RPM that are being described. It's done it once within a minute of my Jeep starting (low speed in parking lot), but usually it's after it's been driven a bit, and it does it more with AC running. It'll do it (so far) a maximum of 5 times in a row. It'll surge and drop a couple times, and you can feel it/hear it through the vehicle. Very noticeable. Happens when driving sometimes, the RPM will surge up, and you will feel it a little bit, and when i am nearing full stop, or idling at a light.

So far I have only cleaned throttle body, changed air filter, run gas treatments, and downstream O2.
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Unread 07-18-2013, 11:28 PM   #22
hardbodyjeep
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Quote:
Originally Posted by NewtoZJ View Post
Mine has the same surges and drops in RPM that are being described. It's done it once within a minute of my Jeep starting (low speed in parking lot), but usually it's after it's been driven a bit, and it does it more with AC running. It'll do it (so far) a maximum of 5 times in a row. It'll surge and drop a couple times, and you can feel it/hear it through the vehicle. Very noticeable. Happens when driving sometimes, the RPM will surge up, and you will feel it a little bit, and when i am nearing full stop, or idling at a light.

So far I have only cleaned throttle body, changed air filter, run gas treatments, and downstream O2.
Yeah idk man mine does it all the time its very annoying but determined to fix it ill keep posting and letting everyone know what I do and how it affects the problem but TGIF. Paycheck = parts lol
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Unread 07-18-2013, 11:33 PM   #23
dellis
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1998 ZJ 
 
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Location: Vienna, VA
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hardbody, do you have access to a mityvac or some other type of vacuum tester? The reason I ask is that I am wondering what your vacuum measurement is on your intake manifold, and if you have another vacuum leak somewhere.
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Unread 07-18-2013, 11:54 PM   #24
hardbodyjeep
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Quote:
Originally Posted by dellis View Post
hardbody, do you have access to a mityvac or some other type of vacuum tester? The reason I ask is that I am wondering what your vacuum measurement is on your intake manifold, and if you have another vacuum leak somewhere.
No I don't. I wish I did would make this a lot more easy I'm gonna continue looking for them over the weekend and maybe have a friend help me look
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Unread 07-26-2013, 04:45 PM   #25
hardbodyjeep
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Ok soo I know its been awhile but just giving a update I put a new tps sensor on today didn't help my problem also got crank shaft position sensor ill be putting that on tomorrow soo ill keep everyone postedjust gonna throw parts at it till its fixed but atleast ill know everything is new
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