Low RPM while idling
- Thread starter box12360
- Start date
Curious too. Yours is exactly like mine. And at those RPM it isn’t smooth. The mirrors shake etc. I too cleaned the TB and IAC etc. changed spark plugs too.
My 05 Sport 6 speed manual idle was around 700 to 750 when purchased in Sept.
After replacing bad 02 sensors and installed new spark plugs and cleaned the idle control valve it now idles around 550.
Edit: my 4.0 6 speed with 105k idles smoothly around 550 rpm..
My 2.5L with 169k idles smoothly around 800rpm. Never seen it get below 750 rpm, it's a 3 speed automatic.
After replacing bad 02 sensors and installed new spark plugs and cleaned the idle control valve it now idles around 550.
Edit: my 4.0 6 speed with 105k idles smoothly around 550 rpm..
My 2.5L with 169k idles smoothly around 800rpm. Never seen it get below 750 rpm, it's a 3 speed automatic.
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garrett2112
New Member
I went with the
Autolite XP985 Iridium XP Spark Plug
Gapped .035
They seem to run really well. The old spark plugs I took out were .025+ over on the gap.. It idles better now for sure.
I have a 2001 4.0L with 3-speed auto and at start-up my RPM's jump close to around 1500 then immediately comes back down to around 750-700. When fully warmed up it idles smoothly right at 500 RPM's.
garrett2112
New Member
It still "rumbles" when idling and you can see the fluctuation in the gauge needle go up and down i would saw 25-50 RPM. Not smooth.... almost like a very mild cam in it which there is not.
I plan on taking the Throttle body off and really scrubbing everything down.
My idle is that low as well when warm, which I thought was pretty low as every other manual I have ever owned was probably 700 or so when warmed up.
But it's smooth, doesn't make any noise except when I have the clutch depressed, there's a slight rattle there but I'm not concerned.
But it's smooth, doesn't make any noise except when I have the clutch depressed, there's a slight rattle there but I'm not concerned.
garrett2112
New Member
Couple days ago I actually put in new pcv rubber gourmets and elbows. I did notice on the rear PCV elbow connection going to the i think intake (picture below larger of the two), there was a tear in the bottom of the female rubber connection(again pic below) that connects to the pcv elbow. It was a little more than 1/4 inch. In the process of replacing it but for now i put on a hose clamp right after the tear to get a seal.
Idle roughness is still the same....
garrett2112
New Member
Release the tension on the serpentine belt and turn the pulley by hand.
You can tell if it is binding or hard to turn.
A new idler pulley is $33 from wermopar.
Well I finally solved the lower idle issue as well as the motor occasionally not starting after a driving for awhile (when its warm) and it would also misfiring in a cylinder when cranking up for 10-20 seconds.
Unbeknownst to me my motor did not have the heat sheild between the manifold/exhaust and the fuel rail/injectors. I also added the #3 injector heat sheild as well. It runs like a different Jeep in a good way! Idles better-smoother-couple hundred RMP higher. In reference to the first picture in the post it idles at the dot below the 1K mark. Very happy with the heat sheild and injector sheild to combat heat soak.
Unbeknownst to me my motor did not have the heat sheild between the manifold/exhaust and the fuel rail/injectors. I also added the #3 injector heat sheild as well. It runs like a different Jeep in a good way! Idles better-smoother-couple hundred RMP higher. In reference to the first picture in the post it idles at the dot below the 1K mark. Very happy with the heat sheild and injector sheild to combat heat soak.
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Idle looks like 650rpm which is fine. Most 4.0s I've seen are rough at idle. New motor mounts can help keep it smooth.