Birty Dastards Jeep Club

Tech Forum => Workshop => Topic started by: Brynjaminjones on July 28, 2014, 11:45:11 PM

Title: Engine hunting when coasting
Post by: Brynjaminjones 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?

Title: Re: Engine hunting when coasting
Post by: Delk 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.

Title: Re: Engine hunting when coasting
Post by: j33pky on July 29, 2014, 09:08:52 AM

I think this lemon of a car should be bought by me for £50

Title: Re: Engine hunting when coasting
Post by: gazjeep 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.

Title: Re: Engine hunting when coasting
Post by: wildwood 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.

Title: Re: Engine hunting when coasting
Post by: Brynjaminjones 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.

Title: Re: Engine hunting when coasting
Post by: Dave69 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

Title: Re: Engine hunting when coasting
Post by: Brynjaminjones 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.

Title: Re: Engine hunting when coasting
Post by: gordy 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/