Is 500 rpm too low for idle? - Page 3 -
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post #31 of 36 Old 01-27-2013, 04:30 AM
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1994 ZJ 
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Originally Posted by kb9mfd View Post
...after cleaning the IAC, the idle does not change when put under load (like the A/C pump or putting it in drive)...
Normal, that's the purpose of the IAC.

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post #32 of 36 Old 01-27-2013, 01:23 PM
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mine does the same thing but it came out of no where and now when i put it in reverse the whole thing locks up tranny and motor any idea what it could be ?
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post #33 of 36 Old 02-27-2014, 05:35 AM
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1995 ZJ 
Join Date: Feb 2014
Location: Ft. Lauderdale
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whole jeep vibrates when under load

I just got a 4.0 95 ZJ, it starts great but when shifting out of park or neutral the jeep would vibrate like crazy. It would run and settle down just fine until I'd come to a stop sign or light then, while braking, the vibration would begin again and sometimes cut out or stall.
Checked drivetrain, exhaust, mounts and the codes. No check engine light. Watched a youtube that sort of described my problem and the fix was to replace the throttle position sensor (TPS) while being careful not to mess with the throttle body by cleaning it or moving the throttle. (sometimes that causes the PCM to mess up the learned idle apparently resulting in an abnormally high idle situation.
I did as the video instructed and picked up a new TPS at Advanced Auto for around $40. Put it on (simple 2 torx bolts) and the jeep ran just fine. No more vibration or stall. Happy as a clam here although at some time in the future I plan to clean the throttle body, etc. Hope this might help someone since I had a hard time figuring this out and I have the service manual which wasn't much help in that regard.
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post #34 of 36 Old 02-27-2014, 05:38 AM
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low idle lead to my fix

I forgot to add that I noticed a very low idle of 300-400 rpms when I was having my vibration and stall which led me to my fix. It now idles at 600 rpms which seems to be working out for me for now.
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post #35 of 36 Old 02-27-2014, 03:21 PM
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Originally Posted by PolkaPower View Post
700-800 is normal. Possible bad IAC sensor.
mmm, get 550-ALMOST 600 solid, all the time and i cleaned my IAC last summer it was still good ! .. for 4.0's its normal like that i think

if its colder outside it will stay a bit up and slowly drop to 500-550
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post #36 of 36 Old 09-12-2016, 10:42 AM
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Hey fokes sorry I have a 98 zj that was having horrible idle issues I change the inc and I didn't bother cleaning it due to the spring does wear down but after installing it I noticed a solid idle and it's a 25 dollar part at auto zone and a 5 min install save yourself some time and try this first
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engine , idle speed

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