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Unread 04-06-2014, 09:37 PM   #1
jfrancx
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Low, fluctuating idle when engine is warm

Hi everyone,

having gone through 20,000 posts to try and find my problem I ended up making my own post.

Here's the story:

I drive a Jeep Grand Cherokee 3.7 Laredo with about 90.000 miles. About half a year ago I noticed that only when my car engine is warm, it would have a pretty low idle in my opinion at stops, at that point fluctuating around 650 rpm. Now, since a 2 weeks my rpm is fluctuating mildly between 450-550 rpm. I must also mention that there is no Check Engine Light whatsoever. Other things that might help you guys out: occasionally when flooring my car, it'll take 2-3 seconds for the car to react and go.

I have tried checking for vacuum leaks using carb cleaner but having no experience whatsoever (though very eager to try) working on cars Im not sure if everything I did was correct. Anyways, the things I found online:

-PCV something (no idea what this is)
-dirty IAC valve (done most research on this and how to clean it but havent done it yet because I wanted to pick your brains first)
-dirty Throttle body (same story as above)
-TPS sensor
-Vacuum leaks (though online this is usually shown by a high rpm instead of low?)
-EGR valve

The car hasn't stalled yet but with the decreasing rpm's I fear this might not take long anymore, 2 days ago I saw it go as low as 300 rpm before going back to fluctuating between the 450-550.

Since I'm going to Miami in 2 weeks (I live on an island in the middle of the ocean which doesnt have many carparts available) I wanted to know your opinions.

Thanks in advance to all of you for taking the time to read this.

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Unread 04-06-2014, 11:26 PM   #2
trax95008
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Dirty throttle body is most likely, and should be the first place you start
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Unread 04-07-2014, 04:02 AM   #3
caulk04
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Agreed. Clean the TB thoroughly, be sure to get the IAC and it's ports cleaned as well.

Next step for me would be to replace the IAC, then the TPS.
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Unread 04-07-2014, 08:16 AM   #4
bhawks28
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I think I'm experiencing the same problem as you.s
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Unread 04-07-2014, 09:59 AM   #5
Kapoosta
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Check transmission oil level as well. Mine had a leak and I had about 2 quarts of fluid missing and it was idling low.
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Unread 04-07-2014, 10:02 AM   #6
BonesWK
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I had constant up and down 400 or so to 600 rpms. Changed Throttle Position Sensor and it runs fine.
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Unread 04-07-2014, 03:31 PM   #7
jfrancx
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Thanks to all of you! I'm going to start off replacing the TPS which is the more expensive option compared to cleaning the throttle body but due to my severe lack of experience in working with engines I think its a safer bet to try doing this first. If that doesnt work ill try somehow cleaning the throttle body and otherwise replacing the iac as well. Ill keep all of you up to date seeing as theres nothing more frustrating as unsolved threads.
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Unread 04-09-2014, 05:30 AM   #8
No5pam
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I have the same problem. So far, I have changed the oil (2x. I've had my jeep < 6 months, and have not put 4k miles on her yet). I changed the PCV valve, replaced the air filter, new plugs, (I *think* my trans fluid is good), (in that order, mostly for ease of completion and cost) changed the rear diff fluid, flushed the radiator and just last week I cleaned my TB see B/A pics here (http://www.jeepforum.com/forum/f67/w.../index795.html). I *still* have the problem. Up next, I think, is the IAC. It's like $70, so I haven't done it yet. Seems like I read somewhere that a bad/aging idle air controller is the number one cause of low idle/stalling -but you know the Internet; you can't believe everything you read. It probably says out there somewhere that I *don't* like beer!

Don't let a
Quote:
Originally Posted by jfrancx View Post
... severe lack of experience in working with engines...
stop you. If you screw something up, someone out there can UNscrew it for you. Nothing ventured, nothing gained! Cleaning the TB was *super* easy. It cost me 30 of time, and I didn't have to spend ANY beer money!
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Unread 04-09-2014, 05:35 AM   #9
BlkJeepTJSahara
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Gotta love ethanol in our gas.. Imagine what everthing will look like when they decide to go to 20%
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Unread 04-10-2014, 05:26 AM   #10
No5pam
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Quote:
Originally Posted by BlkJeepTJSahara View Post
Gotta love ethanol in our gas.. Imagine what everthing will look like when they decide to go to 20%
Yea. Like high fructose corn syrup, they're both made from corn.
Not good for humans. Not good for gas.
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Unread 04-10-2014, 02:45 PM   #11
jfrancx
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Quote:
Originally Posted by No5pam View Post
Don't let a stop you. If you screw something up, someone out there can UNscrew it for you. Nothing ventured, nothing gained! Cleaning the TB was *super* easy. It cost me 30 of time, and I didn't have to spend ANY beer money!
It was indeed easier as expected but me being born with two left hands I'd probably be able to put my car on fire while washing it.

Okay so I decided to also clean my TB. Opened it up, cleaned the butterfly and paid special attention to where it touches the sides of the TB. I did all this with the battery disconnected. After that I attempted to clean my IAC valve but the screw was stuck so didnt manage to open that up. I will try next time with a better tool for the job. Started the car after reconnecting battery, drove a bit, problem persists. It even feels a bit rougher, can this be due to flashing the ECU?

So whats the next most likely culprit?

TPS or IAC?

Thanks guys.

Last edited by jfrancx; 04-10-2014 at 03:03 PM..
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Unread 04-10-2014, 04:00 PM   #12
jfrancx
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By the way guys, I just read this:

Hey I was talking to a buddy of mine who owns a 2006 jeep WK 3.7 V6 and he said he was having rough idle only when his jeep was warmed up to operating temp he said the idle was shaky and below 500 rpm he replaced pretty much everything under hood lol, than he replaced the oxygen sensors and it cured his issues, he said that the jeep runs closed loop meaning it takes previous info to operate when cold and when warm it runs open loop where it uses the current sensors, and he said cold the o the. Sensors weren't feeding PCM info, but when there warmed up that gave bad info.

Any thoughts on this?


PS I recleaned the TB a bit more extensive by spraying it all over inside the TB and airhole to the IAC. I know have worse idle and a gigantic oil leak?? Could the oil leak cause the low idle maybe?

Last edited by jfrancx; 04-10-2014 at 06:16 PM..
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Unread 04-11-2014, 09:39 PM   #13
Kapoosta
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Where is the oil coming from? Transmission oil is reddish, engine oil, transfer case oil, differential oil will all be brownish or black (depending on when they were last changed). If you have low transmission oil you will have a low/rough idle. Make sure you follow the correct procedure to check the oil level or else you will never get the right reading.

I have started a thread for idle issues here:
http://www.jeepforum.com/forum/f67/general-thread-idle-problems-fixes-2317489/#post22063465

Maybe it can help.
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Unread 04-12-2014, 09:27 AM   #14
No5pam
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Quote:
Originally Posted by No5pam View Post
....Up next, I think, is the IAC. ...Seems like I read somewhere that a bad/aging idle air controller is the number one cause of low idle/stalling...

[QUOTE=jfrancx;22029825] but me being born with two left hands I'd probably be able to put my car on fire while washing it./QUOTE]

That's funny!
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Unread 05-21-2014, 10:51 AM   #15
Rob_S
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When you guys clean the TB are you removing the TB to clean? Or are you just wiping it down with it installed? I need to do this to my wife's WK but keep finding an excuse to put it off. LOL.
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