Rough Idle

THrough the past few weeks i have had a rough idle. The jeep accelerates/drives fine but just the idle feels funny. When i am in the car it kinda has a small jerk every 5 sec . I dont think its a miss. Recently i have changed these items and it has helped but its still there a small bit.

1. bosch 02 sensor
2. napa map sensor
3. dumped a bottle 20oz of techron concentrate cleaner
4. cleaned IAC (idle air controller)

In the past 6 months these things have been done:
1. fuel filter
2. oil change + filter
3. spark plugs (champion) and wires (bosch)
4. tps

THanks guys any info would be helpful

pete

ohh this is only felt happening during idle regardless of tranny gear (auto)..
pete

I have usually found that a rough idle can be addressed by either wires, plugs, or injector cleaner. You may also need to run several consecutive injector treatments. I once used two techron treatments to no avail and then tried valvoline cleaner which, in turn, solved the rough idle. I am unsure if the techron was ineffective or it just required three treatments to solve the rough idle. You might also check for a cracked distributor cap.

The absolute best fuel system cleaner is BG44K. It runs around $20 a can. The other stuff can't hold a candle to it.

What year XJ? I´ve improved my idle with a new cap, caps seem to corrode faster than plugs. If it´s a Renix, check the coil connections, spray them out with contact cleaner and scrubb them a bit, if you can find a brush small enough. I´ve also found corrosion on the contacts between the coil and ignition module.
In fact, cleaning all the grounds has helped mine idle better, by degrees. The more cleaning I do the better it runs.
Is your idle constant or does it fluctuate, up and down.

My 00 XJ has a slightly rough idle, especially when cold. The plugs are new. I recently ran a can of that BG44k and it didn't do squat. The throttle body looks pretty clean from what I can tell.

I had an 88 XJ that ran a little rough too, just figured it was a 4.0L thing.

Anything other things that i can add to my list of trials for when i have a chance.

Someone suggested that i try regapping my plugs, is this useful ?

pete

Checking the gaps would be good... tighten the tensior boltmaybe? My '00 XJ runs a lil rough at idle too, and "kicks" like you described... it's real bad when the A/C is on, pretty much shakes the whole rig, side/rearview are wobblin like I got 2 15" woofers!

I havnt had a chance to look at those items you guys suggested but i noticed something today that might mean something -- At idle the oil pressure needle seems to correlate with the jerk every few 5 or so seconds.

Thought i would say my observation,,gonna do those things suggested tom and report back.

pete

Sounds like a high voltage leak. Carbon tracking in the distributor cap, moisture maybe. You can sometimes pick out high voltage archs at night in the dark (if they are on the outside). Or poke around in there with your finger and find them the hard way :laugh3: Try spraying some contact spray inside the cap and wiping it out. Check to see if there is white or green stuff on the inside high voltage studs and/or they are eaten away some.
One way to check is to put a timing light on each spark plug cable, then aim it at a dark spot, you can see a misfire on a specific plug that way. Helps narrow things down. If it´s just one cylinder giving you trouble.
Corrosion in the coil and ignition control module, will weaken the spark some, as will poor grounds. Which can cause periodic no fires, in random cylinders.

Whats contact spray ? Would i just spray some wd40 on the cap and rotor to clean them ?

pete

jeepsrock said:

Whats contact spray ? Would i just spray some wd40 on the cap and rotor to clean them ?

pete

Click to expand...

Contact spray is just a solvent, that loosens corrosion and is fairly plastic friendly. You can most times use brake cleaner also. You want to wipe it out with a paper towel or clean rag, the inside of the distributor gets a coating of carbon (dust). Not much will disolve the corrosion though, the white and green coating from oxidation on the studs and rotor tip.
WD40 is OK for high voltage parts, even mostly for battery voltage parts, but not good for sensor connections. WD40 leaves a coating of light oil and wax.
Whatever you use, wipe it out after applying or you´ll most likely just move the carbon dust around and not remove it.

Today i did a few things and they didnt help as the jerky idle is still there. I replaced the plugs and gapped them to .035 . I cleaned all terminals (battery , grounds, coil). I opened the cap/rotor and cleaned them both up. Cleaned out the connectors for the tps, iac and cps.

Any other ideas..

pete

Take a look at your spark, light colored and splashes or mostly blue and crisp. You can plug off most any vacuum line but the MAP, one at a time and see if things change. Very low idle can cause a miss. What color were your plugs when you pulled them? Too lean or to rich, mostly too rich causes a miss at idle.
I´d check the easy stuff first. Then the rare stuff. Any bottom end noises? Unequal compression. Worn connecting rod bearings and/or unequal compression will make the motor shimmy shake. Messes with the balance some. Sometimes causes the timing chain and distributor to jerk a bit, amplifies the whole thing.
I've listened to my injectors cycle before, you can actually hear them miss a beat or stick, with a piece of tubing.
I put in a new O2 sensor, sure added a lot of zip to the old beast, but idled like chit, finally decided to buy another, had a hunch. Idle smoothed out a lot. I now have a near new spare O2 sensor.
Spray the bottom end connectors with a solvent, scrub them with a very small brush. Easier if you pull the air filter box.
I had a fairly low mileage 87, that had a miss at idle, I never did find the cause, learned to live with it.
My 88 now idles good, dirty bottom end connectors. Cleaning the bottom end connectors really well, even seems to have eliminated my hot starts (2500 RPM surge occasionally at start up).

Well i guess i would try and replace O2 sensors. i put new plugs into mine and im still having issues. im going to check my battery connectors and check out some O2 sensors. from what i hear its best to goto the dealer for them.

If you look at my original posting it states the items i changed one being thr 02 sensor.

pete

I made an interesting observation today, i am not sure if this means anything. When i first start the jeep (cold start) it idles at 1000RPM and is pretty smooth. Its when it gets warm it goes to 650-750 RPM and it startes to jerk. Is this idle when warm to low ? Whats the norm ?

pete

I have a similar problem with my 97. It is just an occassional blip in the idle and comes back down. I also had the pinging under load. I have replaced all the electrical components as you have except for the O2 sensor. I tried Sea Foam through the intake and gas and it did nothing. A Jeep dealer recommended the BG 44. He had me run one can through a half tank of gas and the pinging was gone.The idle however is about the same.

What other sensors, can be responsible for a idle that feels funny ?

pete

jeepsrock said:

What other sensors, can be responsible for a idle that feels funny ?

pete

Click to expand...

MAP sensor.