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Unread 01-26-2008, 10:25 PM   #1
Gsmyth75
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1992 XJ Cherokee 
 
Join Date: Jul 2006
Location: Sarasota, FL
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Jeep surges while driving/ wont idle properly

I recently had yet another freeze plug come out on me, and after reassembling my intake and exhaust manifolds my jeep just seems to not want to idle, and when i get it going down a road it will feel like i let off the gas and then surge forward as if im bliping the throttle, when my foot doesnt move. I thought maybe i had a leak or something in my intake manifold but i took it all apart again and reassembled it all only to still have this problem, I know all the sensors are reconnected. No check engine or anything. My only guess is bad injector o-rings which looked torn up and im going to replace tomorrow, anyone have any other guesses as to why it is running funky?

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Unread 01-26-2008, 10:28 PM   #2
SmrtJustin
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This all happens when you're foot is off the gas, correct? If so, I would guess it's your Idle Air Control (IAC).
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Unread 01-26-2008, 11:05 PM   #3
mickdawg777
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Fuel filter been replaced lately? Sounds like a TPS fluctuation in voltage levels. Rough idle is caused by sticky IAC's. IAC's do not have anything to do with hesitation/surging at a given throttle position.

Check your plugs, plug wires, cap, and rotor. If the cap is black with carbon on the contacts, chuck it and get new rotor and cap. Same for the plugs and wires.
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Unread 01-26-2008, 11:38 PM   #4
SmrtJustin
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Quote:
Originally Posted by Gsmyth75
I recently had yet another freeze plug come out on me, and after reassembling my intake and exhaust manifolds my jeep just seems to not want to idle, and when i get it going down a road it will feel like i let off the gas and then surge forward as if im bliping the throttle, when my foot doesnt move. I thought maybe i had a leak or something in my intake manifold but i took it all apart again and reassembled it all only to still have this problem, I know all the sensors are reconnected. No check engine or anything. My only guess is bad injector o-rings which looked torn up and im going to replace tomorrow, anyone have any other guesses as to why it is running funky?
Idle problems can be caused by the IAC. But after reading your post multiple times, it sounds more like you also have problems while driving, that sounds more like a TPS.
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1999 Cherokee Classic
Deep Amethyst
60,000 miles

Mods:
Dynomax Cat-back
OME CS035RA Heavy Load Rear Leafs (~3.25")
RE 1334 Front Spacers (~2.5")
P.O.R.C. HD SYE
30x9.5 General Grabber AT2s
B&M SuperCooler 70255 and Temp Guage
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Unread 01-26-2008, 11:57 PM   #5
Gsmyth75
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It happens while driving (on the gas) and while just sitting at an idle. I dont think it would be an ignition related thing cause this only happened after I re did my manifolds. And the fuel filter was replaced a short while ago. Im going to try replacing fuel injector o-rings tomorrow, spraying carb cleaner around the intake gasket to see if theres a difference, and try cleaning out/ testing my iac and tps, and resetting the computer. I did take off the two connectors on the throttle body while doing the freeze plugs but i put them back on fine, how easily do they break? could I have damaged it by disconnecting it twice? If this helps while driving it and it started surging I floored it and it didnt kick down to 2nd like it would normally, it only kicked down to 3rd, so I'm leaning more to the tps/iac not working properly.. Thanks for the quick responses this late at night!
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1992 Cherokee Laredo 4.0 L6, Aw4, Dana 30/35, Np242, 201k
Crower p/n 44243 Camshaft, Camsaver High Oiler Lifters, He Pistons .030 Over, Decked Block and MIlled Cylinder Head. Melling High Volume Oil Pump
Flowmaster Super 40/ Cat and Tailpipe Delete, Apn Header, Homebrew Bored Throttle Body, Rustys Cold Air Intake with Spacer
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Unread 01-27-2008, 07:21 AM   #6
MattS
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My 99 will do this kind of thing, mostly when the engine is warm. I've replaced TPS, IAC, fuel filter, plugs, caps, and wires. I'm at a loss so post what you find out.
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Unread 01-27-2008, 07:40 AM   #7
HighCountry
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The vacuum line to the Fuel Pressure Regulator is OK?

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Unread 01-28-2008, 07:48 AM   #8
Gsmyth75
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Fixed

Quote:
Originally Posted by HighCountry
The vacuum line to the Fuel Pressure Regulator is OK?

Bruce
Thanks alot man, I had checked the vacuum line, but not the connectors to the line. One of them was cracked beyond belief. A trip to advanced auto to get a new connector fixed all of my weird idle problems. So thanks for saying that which made me double check it. Also it's weird what you find out while tearing stuff apart, now I have a couple more projects.
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1992 Cherokee Laredo 4.0 L6, Aw4, Dana 30/35, Np242, 201k
Crower p/n 44243 Camshaft, Camsaver High Oiler Lifters, He Pistons .030 Over, Decked Block and MIlled Cylinder Head. Melling High Volume Oil Pump
Flowmaster Super 40/ Cat and Tailpipe Delete, Apn Header, Homebrew Bored Throttle Body, Rustys Cold Air Intake with Spacer
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Unread 01-28-2008, 10:58 AM   #9
collkid
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And where is that fuel pressure regulator? anyone?
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Unread 01-28-2008, 09:49 PM   #10
Gsmyth75
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Quote:
Originally Posted by collkid
And where is that fuel pressure regulator? anyone?
On my `92 look for a vacuum line going from the intake manifold to the fuel rail (with the injectors on it), and it's where the vacuum line connects.
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1992 Cherokee Laredo 4.0 L6, Aw4, Dana 30/35, Np242, 201k
Crower p/n 44243 Camshaft, Camsaver High Oiler Lifters, He Pistons .030 Over, Decked Block and MIlled Cylinder Head. Melling High Volume Oil Pump
Flowmaster Super 40/ Cat and Tailpipe Delete, Apn Header, Homebrew Bored Throttle Body, Rustys Cold Air Intake with Spacer
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Unread 01-29-2008, 06:04 AM   #11
SmrtJustin
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The fuel pressure regulator is in the tank.
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1999 Cherokee Classic
Deep Amethyst
60,000 miles

Mods:
Dynomax Cat-back
OME CS035RA Heavy Load Rear Leafs (~3.25")
RE 1334 Front Spacers (~2.5")
P.O.R.C. HD SYE
30x9.5 General Grabber AT2s
B&M SuperCooler 70255 and Temp Guage
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Unread 01-29-2008, 06:32 AM   #12
Gsmyth75
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Quote:
Originally Posted by SmrtJustin
The fuel pressure regulator is in the tank.
Maybe on your `99 but on my `92 i'm pretty sure it's on the fuel rail.
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1992 Cherokee Laredo 4.0 L6, Aw4, Dana 30/35, Np242, 201k
Crower p/n 44243 Camshaft, Camsaver High Oiler Lifters, He Pistons .030 Over, Decked Block and MIlled Cylinder Head. Melling High Volume Oil Pump
Flowmaster Super 40/ Cat and Tailpipe Delete, Apn Header, Homebrew Bored Throttle Body, Rustys Cold Air Intake with Spacer
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Unread 02-05-2008, 08:33 PM   #13
SmrtJustin
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Quote:
Originally Posted by Gsmyth75 View Post
Maybe on your `99 but on my `92 i'm pretty sure it's on the fuel rail.
You are correct. I apologize for that, somehow I got mixed up and thought you had a newer XJ.
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1999 Cherokee Classic
Deep Amethyst
60,000 miles

Mods:
Dynomax Cat-back
OME CS035RA Heavy Load Rear Leafs (~3.25")
RE 1334 Front Spacers (~2.5")
P.O.R.C. HD SYE
30x9.5 General Grabber AT2s
B&M SuperCooler 70255 and Temp Guage
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Unread 04-28-2008, 11:09 AM   #14
firerescue251
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I am having the same problem as the first post on this thread. I have replaced o2 sensors, IAC, tested the tps and it came back with .91 ohms at a closed throttle and 4. something at WOT. Done a vacuum test which was inconclusive due to the fact that it didn't exibit the problem, of course, when i did the vacuum check. I'm running out of choices.....
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Unread 04-29-2008, 04:09 PM   #15
jcrowley
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new plugs, wires, rotor button dist cap, new tps...no luck. i've done fuel pressure test...it's solid at 49 or so psi. i'm at my whits end with this thing. i've haven't done a fuel filter change in awhile, but i'm hestitant to do that just yet not really knowing what the problem is.
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