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Author Topic: Engine hunting when coasting  (Read 2828 times)

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Brynjaminjones

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Engine hunting when coasting
« on: July 28, 2014, 11:45:11 PM »
A very boring question, but I've noticed that when coasting in drive the engine RPM hunts around between about 900 and 1200.
I'm guessing that's not normal... what's up with it?
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Delk

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Re: Engine hunting when coasting
« Reply #1 on: July 29, 2014, 08:52:18 AM »
The idle speed is also tied in with the vehicle speed sensor. At stop you should be around 900 and above this it runs at 1100 to 1200.
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j33pky

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Re: Engine hunting when coasting
« Reply #2 on: July 29, 2014, 09:08:52 AM »
I think this lemon of a car should be bought by me for £50
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gazjeep

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Re: Engine hunting when coasting
« Reply #3 on: July 29, 2014, 09:15:42 AM »
Possibly the O2 sensors & or TPS.

Had to replace all over the above after Harptree & the associated drowning in chocolate.
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wildwood

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Re: Engine hunting when coasting
« Reply #4 on: July 29, 2014, 09:55:40 AM »
Bro in law currently has that happening on my ex GC..........have yet to get my hands on but from answers I got here fuel pressure, TPS and O2 sensor....... As Gaz said.

Diagnostic plug in to read codes might help.
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Brynjaminjones

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Re: Engine hunting when coasting
« Reply #5 on: July 30, 2014, 01:27:32 PM »
This seems to be very temperamental, which is annoying. I do have another symptom though:


Sitting in traffic yesterday with transmission in Drive, Jeep was running perfectly at normal hot idle. I eventually put it into neutral, and it instantly jumped to about 1100 rpm. Change back to drive and it went back down again. I tried a few times and it did the same every time, but I've not been able to replicate it since then.
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Dave69

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Re: Engine hunting when coasting
« Reply #6 on: July 30, 2014, 07:08:56 PM »
a possible solution is to clean the mass air flow sensor in the air intake. rising revs once in neutral is normal
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Brynjaminjones

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Re: Engine hunting when coasting
« Reply #7 on: July 31, 2014, 01:13:23 AM »
Cheers Dave, will clean that. I'm aware of them rising slightly, but this was much more than normal.
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gordy

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Re: Engine hunting when coasting
« Reply #8 on: July 31, 2014, 09:09:42 AM »
Another thing I would do is remove and thoroughly clean the IAC valve, its on the throttle body.

http://www.jeepforum.com/forum/f13/how-clean-your-idle-air-control-valve-756934/
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