post #1 of Old 01-20-2013, 08:56 AM Thread Starter
kb9mfd
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1995 ZJ 
 
Join Date: Dec 2012
Location: Janesville
Posts: 81
Is 500 rpm too low for idle?

I am wondering if this is normal or I have something I need to look into. While in park or neutral it idles just fine around 700~800 rpm, its smooth and quiet. When I put it in gear or when I stop while driving, the rpm drops to around 500 rpm and it shakes and causes the whole truck to vibrate. I assume that is because of the low idle. Its not pulsing, missing, or erratic, just a steady vibrate. I am wondering if that is normal, or its idling too low, and if it is too low what to look for. The pcm is not reporting anything so I assume the sensors are fine. I just got it a couple of months ago and its the first jeep I have owned so I am not sure if its normal. (its a 4.0 I6) Thanks! - Jeremy

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post #2 of Old 01-20-2013, 10:07 AM
jnowak
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1993 ZJ 
 
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Location: dahlonega
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Mine does the same. Gonna subscribe to see the suggestions. I have done all the standard cleaning. All I can come up with is its a combination of a iac on its way out and motor mounts worn out.
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post #3 of Old 01-20-2013, 10:20 AM
papitt
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1995 ZJ 
 
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Location: Stephenville Texas 76401
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I'm going to say your about too need a torque converter. When it's at 500 does it fell like it is pulling more or that you have to press on the brake more than you should. TQ time.
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post #4 of Old 01-20-2013, 05:36 PM
rcMikeS1990
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1994 ZJ 
 
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Location: Lincoln
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I don't know about the 4.0s idle, but my 5.2 idles incredibly low

2013-01-07-14.32.12.jpg



2013-01-05-19.43.37.jpg

Two different days, same low idle

1994 Grand Cherokee Limited 5.2L V8 318, Spectre cold air intake, Flowmaster Super44 muffler to 3.5" resonator tip, 30x9.5 BFG A/T's, Custom Tranny and TC shifter mod
My Build Thread--not sure how to make that the link-http://www.jeepforum.com/forum/f13/my-build-thread-1568707/
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post #5 of Old 01-20-2013, 05:51 PM
ZeeJay1997
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I'm not certain the same thing happens on OBD1 units, but my tach lags about 150 rpms behind what the PCM reports to a scanner.
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post #6 of Old 01-20-2013, 07:19 PM
Bigdjs123
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Location: Parma
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Mine does the same too
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post #7 of Old 01-24-2013, 04:19 PM Thread Starter
kb9mfd
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Location: Janesville
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After some other looking around, 600 seems to be the norm. I read somewhere about cleaning the IAC, so I tried that and it now just idles around 600 and does not drop after shifting into gear, but it still shakes/vibrates. I guess I will count that as being old engine mounts. Since its a 95 I'm sure they are a little hard, and since its cold out they are probably even stiffer. - Jeremy
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post #8 of Old 01-24-2013, 04:51 PM
Proph2010
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Location: Martinsburg
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Quote:
Originally Posted by rcMikeS1990
I don't know about the 4.0s idle, but my 5.2 idles incredibly low

Two different days, same low idle
Mines is identical to your, no vibrations or anything abnormal either.
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post #9 of Old 01-24-2013, 06:50 PM
kyle_outrage
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1995 ZJ 
 
Join Date: Jan 2013
Location: lake orion
Posts: 11
mine idles at 500 aswell but mine only shakes if im low on oil. everyone I know or have talked to has said that their 5.2 idled around 500
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post #10 of Old 01-24-2013, 10:11 PM
papitt
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... Mine is a 6Cyl not the 5.2 But how low on oil is yours when it viberates .. My VIC says to check the oil .. but it's not low I checked it tonight . maybe a quarter qt low.. . What kind of oil do you run to keep it from vibrating or going low.
.. . I was about to swap mine over to Motor craft synthetic blend because I have a bunch of it. DO YOU SEE ANY ISSUES WITH IT.
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post #11 of Old 01-24-2013, 10:33 PM
Candymancan
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1998 ZJ 
 
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Location: Virginia
Posts: 4,987
Our 4.0 and 5.9 idle at about 500 rpms both.

2013 6.2 V8 Camaro SS 30k
98 5.9 V8 ZJ 180k
98 4.0 I6 ZJ 240k
90 5.9 SJ Grand Wagoneer 110k
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post #12 of Old 01-25-2013, 08:34 AM
PolkaPower
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1998 ZJ 
 
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Location: The Abyss
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Mine sits right here below this mark.
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post #13 of Old 01-25-2013, 08:57 AM
Myusername1674
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1995 ZJ 
 
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Location: Chattanooga
Posts: 2,310
Quote:
Originally Posted by rcMikeS1990 View Post
I don't know about the 4.0s idle, but my 5.2 idles incredibly low

Two different days, same low idle
Thats exactly how my 318 idles, low as can be. My friends got a 90's chevy 350 and it idles that low to. I think it may just be an old engine thing to do. Lol

95 FiveTwo ZJ, DD, Lifted, Locked on 35s, Build (in progress)

My 5.9 swap (in progress)

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post #14 of Old 01-25-2013, 09:31 AM
FAlfani81
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1993 ZJ 
 
Join Date: May 2012
Location: Lindenhurst
Posts: 359
Quote:
Originally Posted by kb9mfd View Post
I am wondering if this is normal or I have something I need to look into. While in park or neutral it idles just fine around 700~800 rpm, its smooth and quiet. When I put it in gear or when I stop while driving, the rpm drops to around 500 rpm and it shakes and causes the whole truck to vibrate. I assume that is because of the low idle. Its not pulsing, missing, or erratic, just a steady vibrate. I am wondering if that is normal, or its idling too low, and if it is too low what to look for. The pcm is not reporting anything so I assume the sensors are fine. I just got it a couple of months ago and its the first jeep I have owned so I am not sure if its normal. (its a 4.0 I6) Thanks! - Jeremy
Mine does the same. Idle is at about 500ish but I don't get any vibrations.

7 to 800 sounds a little high to me.

Maybe your exhaust it rubbing on something.
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post #15 of Old 01-25-2013, 09:37 AM
PolkaPower
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Quote:
Originally Posted by FAlfani81 View Post
Mine does the same. Idle is at about 500ish but I don't get any vibrations.

7 to 800 sounds a little high to me.

Maybe your exhaust it rubbing on something.
700-800 is normal. Possible bad IAC sensor.
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