Rough Idle

gingerchocolate

gingerchocolate

Member
My 07 JK is having and interesting idle issue.

It feels more like a misfire, but I have no codes.

Wires are about a year old (i checked them and are fine). However, I had an issue a while back with the #4 boot burning up and arching. I suppose the coil could be damaged but I don't have a loss of power, at least a noticeable one.

I run 91 top tier fuel. I just filled the tank and added Lucas injector treatment, so we'll see if that changes anything.

I'm just kind of stumped as there's only an issue when at idle (stopped or in park). My idle RPM right now is around 500-600.

Tomorrow I'm going to clean the TB. What else should I look for?

Again it's only when stopped or in park, otherwise the Jeep feels right.
 
jeeeep

jeeeep

Hooked
gingerchocolate said:
My 07 JK is having and interesting idle issue.

It feels more like a misfire, but I have no codes.

Wires are about a year old (i checked them and are fine). However, I had an issue a while back with the #4 boot burning up and arching. I suppose the coil could be damaged but I don't have a loss of power, at least a noticeable one.

I run 91 top tier fuel. I just filled the tank and added Lucas injector treatment, so we'll see if that changes anything.

I'm just kind of stumped as there's only an issue when at idle (stopped or in park). My idle RPM right now is around 500-600.

Tomorrow I'm going to clean the TB. What else should I look for?

Again it's only when stopped or in park, otherwise the Jeep feels right.
Click to expand...

When was the last time you changed plugs? I'd change the coil if you had issues and a boot arching, you wouldn't notice a power loss so much at speed but more noticeable at idle.

Do you have a tune to adjust timing for 91 octane? if not, no need to run 91 as it doesn't provide any benefit.

I'd pull the plugs - at least #4 and check it, replace the coil and wire at minimum. If you want to upgrade your ignition system, check out Performance Distributors FirePower ignition kit for the JK, uses stock plugs with wider gap. If you have a tuner and can use it to tune for higher octane performance then I'd run 91, otherwise save some money and just run regular.
 
wayoflife

wayoflife

Administrator
Staff member
jeeeep said:
Do you have a tune to adjust timing for 91 octane? if not, no need to run 91 as it doesn't provide any benefit.
Click to expand...

Actually, UNLESS he has his tune set for 91, he really NEEDS to be running 87 as that's what the 3.8L motor is made for. Running too high of an octane WILL cause issues.
 
jeeeep

jeeeep

Hooked
wayoflife said:
Actually, UNLESS he has his tune set for 91, he really NEEDS to be running 87 as that's what the 3.8L motor is made for. Running too high of an octane WILL cause issues.
Click to expand...

that's what I said, if he doesn't have a tune to run 91 there is no benefit to using 91
 
wayoflife

wayoflife

Administrator
Staff member
jeeeep said:
that's what I said, if he doesn't have a tune to run 91 there is no benefit to using 91
Click to expand...

Oh, I know and I hope you didn't misunderstand me. I was agreeing with you and was just trying to underscore what you were saying.
 
gingerchocolate

gingerchocolate

Member
Yes I'm running a tune for 91.

I Checked the plugs, they all look good. I changed the plugs the same time I did the wires. I MAYBE have 10k on both the plugs and wires.

I suppose its worth mentioning that I have Gibson Headers. (I know, I Know:( ) I have more heat protection than I care to admit.

I was just out and it's not consistent. It's like a hiccup.
 
xrocknrollx

xrocknrollx

New member
Have you checked the MAP sensor?

My tj had similar issues where idle would be sporadically low 400-600rpm when stopped and it turned out to be a bad manifold absolute pressure sensor.
 
jeeeep

jeeeep

Hooked
as xrock mentioned I'd look at the maps sensor, I'd also pull the camshaft sensor and check it - it's easy to swap
 
gingerchocolate

gingerchocolate

Member
SOLVED.

Because I have the Gibson headers I have to have heat shielding around my wires near the boot. The shielding is fiberglass with a foil. After cleaning the TB, checking the MAP sensor and Camshaft position sensor with no change I decided to wait until it was dark to see if was any arching that I couldn't see. Sure enough there were these tiny little arc's dancing around the foil along the drivers side 3 plugs. I removed the heat-shields and boom smooth idle.

Thank you all for your suggestions. I at least know I have a clean TB and my sensors are operating correctly.
 
jeeeep

jeeeep

Hooked
good! the Gibson's must generate a lot of heat but now you may have heat related issues later on by removing the heat shield.

if it's arcing that may mean an issue with the plugs, wire, coil or fuel too rich (I hate these types of issues - so many things to check) and it's finding the path of least resistance to a ground.

A few additional things I would check:

Ground strap to the engine, make sure it's not corroded

plugs, pull the plug arcing and check the gap or ceramic for cracks and the color of the tip - does it look like an even burn? did you use dielectric grease on the ceramic part where it contacts inside the boot?

coil - if you're running the 91 tune, the coil may still not be strong enough to give you the spark needed to burn properly

Check it in the dark again and see if you still see signs of arcing, put a screw driver tip on the block next the plug wire and see if it arcs if so, you've got more puzzle to solve - wear some ground protection, leather gloves and rubber sole shoes!
 
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