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Jeep wk
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Discussion Starter #1
Trying to diagnose the crappy idle I have had ever since I got the jeep. I noticed something interesting the other day the ac compressor engages even when the system is off. Is this supposed to happen?
 

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2005 Jeep Grand Cherokee
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2,807 Posts
If your defrost is on, yes. It uses the evaperator to dry the air out so it does cycle the compressor.

If you have a 4.7l I am sure there may be some thing that might smooth it out, I have never been able to isolate it and it seems to happen on A LOT of 4.7l's in WK's. The fact that there are no codes doesnt mean everything but it is a pretty good indication that at least according to the software everything is within parameters. I noted on a couple I have looked at for myself (my own, and one I fixed a misfire on) that they dont count misfire when idling rough.

I have heard it suggested that with a tuner, raising the idle speed up 50 rpms or so helps to smooth it out.
 

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Jeep wk
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Discussion Starter #3
Great to know. Yes I had front defroster on. I have 3.7 with hypertech I wonder if I can adjust idle on that. Randomly the car shakes while at idle, exhaust shakes also. But when I start moving it drive like a dream.
 

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I had the same problem. I cleaned the IAC motor, it was really dirty and I replaced the TPS sensor only because it broke apart when I tried to take the connector off.
 

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there is a ecm update for the 3.7L for a rough idle/no cel. I don't have any info on it, but my buddy updated mine and it fixed it.
 

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Jeep wk
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Discussion Starter #6
How old is this update? mine was updated about a year ago.
 

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ah yeah then you already got it. had to of. I had the same rough idle as you too. Do you have a aftermarket intake? When I installed mine it seemed to take car of most of it, but the ecm update helped finish it off.
 

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Jeep wk
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Discussion Starter #8
Yes K&N intake
 

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Maybe this will help......maybe not. I have the 4.7 and dealt with a rough idle in the past. It got so bad that I would stall out at stop signs, lights, etc. I changed all of the valves and sensors related to this issue and changed the spark plugs as well. None of these things helped at all. I later removed the throttle body and cleaned it thoroughly.....wouldn't you know...it solved the issue. Now I make sure to clean it every few months or so. Might work for you...might not. Won't cost you anything to try at least.
 

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Jeep wk
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Discussion Starter #10
Thanks for the input already cleaned the throttle body. changed idle sensor and almost every sensor in the car! I have another thread "surging pulsing while driving" that explains everything
 

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There is another post somewhere I remember reading a while ago that pertains to the issue. The guy says it has to do with the teeth of some electrical connection being bent and not making solid contact somewhere. Don't remember which connection though. Seemed like he knew what he was talking about. I'm sure a search will reveal his post. Good luck.
 

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Jeep wk
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Discussion Starter #12
I don't know if this matters but when I accelerate there is a high pitched hissing noise wheni give it gas. Can hear when windows are down.
 

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possible vacuum leak?? that would certainly have an effect on your idle and create that hissing I would think. I'm definitely not an expert (not even close) but I would check all of your hoses.
 

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2007 WK
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sounds like a vacuum leak... have you tried seafoaming it through the brake booster hose?

also i know it was mentioned early about raising the idle with a tuner with the 4.7, that feature only works when sitting in park with the tuner connected.
 

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2008 Grand Cherokee
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720 Posts
Matt they're right it does sound like that after a visual inspection looking for any cracks or dried out hose. Use carb cleaner while the trucks running spray it onto your throttle body following it to the manifold. Then onto the manifold around where it bolts on, and any vacuum hoses. Stay away from your electricals eg.your alternator, fuse boxes etc..you don't If, or when the idle changes go back to that spot, and investigate further.
 

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Jeep wk
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Discussion Starter #16
Thanks guys. Will do. Such a beautiful day to work on the jeep.
 

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Jeep wk
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Discussion Starter #18
Ok guys, so i removed intake, throttle body, vacumn lines and pinpointed the noise to the cruise control servo. for some reason it is making noise when accelerating with the car and even idling i can hear air being sucked into it. to troubleshoot it i disconnected it and plugged both vacumn lines and noise stopped but crappy idle still remains. throttle body is very clean
 

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Jeep wk
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Discussion Starter #19
Its the black cylinder to the left of the battery
 
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