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Old 08-27-2007, 09:48 PM   #1
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an odd idle but runs fine when driving.

hi i got the 2.5 and sometimes when it idles it idles down pretty low and like shakes and chugs kinda. but then it will pick right back up. any ideas what is causing this?

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Old 08-27-2007, 10:07 PM   #2
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is this when it is cold?

i know thats what it is with my carbed engine, but with efi it shouldnt do that, maybe clean all the sensor with sensor cleaner, they should have it at your flaps

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Old 08-27-2007, 10:20 PM   #3
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ya this is when i havent been driving it much. like after hours of sitting. it seems to run and drive fine after it though.
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Old 08-27-2007, 10:24 PM   #4
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hmm osunds like it needs to warm up, liek the old carbed engines b4 it starts to idle nicely, im no mechanic but mayeb your thrmostat is broken and your cooling th engine down b4 it gets up to operating temp??


some one else hlep me out here, im a carb man
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Old 08-27-2007, 10:30 PM   #5
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Are you getting any check engine lights?
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Old 08-27-2007, 10:50 PM   #6
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nope no lights or nothing. i read something in the manual that said it can knock at times at idle and thats nothing to worry about. it said if it still knocks while driving then its a problem.

but i just wanted to make sure on this site.

and i dont believe its the thermostat because the temp guage is working correctly.
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Old 08-27-2007, 10:58 PM   #7
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Try cleaning, or replacing your IAC.
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Old 08-27-2007, 10:58 PM   #8
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the temp gauge could be working correctly and the thermostat not working, they're two different sytems, when you turn your engine on, does the gauge slowly rise over a course of a few minutes or does it sit at c for a minute then suddenly jump up?
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Old 08-28-2007, 06:30 AM   #9
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Check your vacuum lines for cracks. A bad line can give you a rough idle sometimes.

When was the last time you did a tune up (plugs, wires, filters, etc)? Make sure your are squared away with the basics before you dive into changing sensors, etc.
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Old 08-28-2007, 09:27 AM   #10
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I have the 4.0 and have the same type of problem. Mine kinda stutters but it's barely enough to see it in the tach. You can't tell it at all when you are driving, just sitting still. I thought it was the plugs so I changed them out and it didn't change it one bit. Don't know what else to try.
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Old 08-28-2007, 11:35 AM   #11
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Mine does the same thing after I start it. The idle will initially peak and then drop, shutter a little and then level off. It has never stalled so it's on my to-do.

I'm thinking it's related to the MAF sensor or idle air control valve. I have a '90 Brono that is notorious for this only it's much worse. I literally have to hose out the MAF sensor with carb cleaner 3-4 times a year.

I'm still ramping up on my Jeep as far as the details for the engine control systems. I "assume" it has a similar system with a MAF sensor and IAC valve.
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Old 08-28-2007, 03:28 PM   #12
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hmmmm now that i think of it do jeeps have ecm's? cause that could be it too. but i just bought the jeep and it could use a tune up and a new serpentine belt. and i plan on changing the oil this week also so ill pick up a chiltons book and start working so ill let ya know how it goes.
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Old 08-28-2007, 03:37 PM   #13
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Hemmer,

I believe any Jeep with EFI has an ECM (Engine Control Module). That's an expensive item and of last resort to replace.

Get a can of carb. cleaner while you're at the parts store and a can of injector cleaner for your gas tank..
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Old 08-28-2007, 06:23 PM   #14
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do jeeps have egr valves? It sounds to me like the egr is not closing at idle, causing exhaust gas to flow into the intake. That's only supposed to happen while driving. . .
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Old 08-28-2007, 08:41 PM   #15
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thats odd. the ecm for my old sonoma was only like $8 if i remember right. what would i need carb cleaner for? my jeeps a 97.
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Old 08-29-2007, 06:45 AM   #16
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A PCV valve may run $8... The Ignition Control Module (ICM)...aka "the computer" is a whole lot more ~ $500.

The carb. cleaner is used to clean the throttle body assembly (the aluminum component located on top of the engine that mixes fresh air into the engine).

You will need to remove the fresh air supply duct (plastic snorkel) then you can spray the cleaner into the engine while it's running. Be careful - wear goggles and only spray a little at a time around the inside of the bore. The engine will run a little rough till it clears.
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Old 08-29-2007, 09:22 PM   #17
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alright. ya im gettin a pcv valve too. and thanks for the info.

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