Rough idle.
Thread Starter
Junior Member
Joined: Sep 2012
Posts: 42
Likes: 0
From: Olathe Co.
Year: 1997
Model: Cherokee
Engine: 4.0
Ok guys I have a rough idle. I know it's in cylinder 2 and probably 4. I have no spark in those cylinders. The jeep runs fine when revved and driving but idling is bad. I'm gonna replace the cap but after that I'm lost. Also I have and on again off again cylinder 1 misfire. Could it be low compression or just bad injectors. Like I said it runs great down the road. I can keep up with my lil bros xj pretty good and he has 4:56 gears. We've raced and he will pull away but not by much. I'm thinking my compression is fine. I do have to hit the gas to start a lot. Idk if that's related. I'm thinkin bad cap or coil. Possible bad iac bad tps? Idk I'm lost.
CF Veteran
Joined: Jan 2012
Posts: 3,170
Likes: 312
From: Australia
Year: 1997 (RHD)
Model: Cherokee (XJ)
Engine: 4.0 ltr
Well, its time to go and do some work and diagnostics.
You say you have no spark: so you tested it?
If you have no spark, it can be plug, lead, distributor cap/rotor, coil etc
When was your last tune-up? Start with that if unknown or long ago.
Test for spark quality.
Clean out your IAC and throttle body.
You say you have to give it a lot of gas to start: check your fuel pressures.
Check for codes, it might help you in your diagnosis workup.
If you think you have cylinders not firing, may I suggest you address that as a possible start for fixing your rough idle?
You say you have no spark: so you tested it?
If you have no spark, it can be plug, lead, distributor cap/rotor, coil etc
When was your last tune-up? Start with that if unknown or long ago.
Test for spark quality.
Clean out your IAC and throttle body.
You say you have to give it a lot of gas to start: check your fuel pressures.
Check for codes, it might help you in your diagnosis workup.
If you think you have cylinders not firing, may I suggest you address that as a possible start for fixing your rough idle?
Thread Starter
Junior Member
Joined: Sep 2012
Posts: 42
Likes: 0
From: Olathe Co.
Year: 1997
Model: Cherokee
Engine: 4.0
I replaced the spark plugs and wires about 2000 miles ago while trying to run down a bad crank sensor. My mechanic checked fuel pressure and it is low. I checked the spark and I have none. That was several weeks back. I'm gonna check it tonight and do the old fashioned check for a light show. But yes I am going to do a good tuneup. Now for the misfire, that is the cause of my rough idle I am certain.
CF Veteran
Joined: Jan 2012
Posts: 3,170
Likes: 312
From: Australia
Year: 1997 (RHD)
Model: Cherokee (XJ)
Engine: 4.0 ltr
I replaced the spark plugs and wires about 2000 miles ago while trying to run down a bad crank sensor. My mechanic checked fuel pressure and it is low. I checked the spark and I have none. That was several weeks back. I'm gonna check it tonight and do the old fashioned check for a light show. But yes I am going to do a good tuneup. Now for the misfire, that is the cause of my rough idle I am certain.
2) And yes, your lack of spark on one or more cylinders is a HUGE possible cause for your rough idle....so
start doing something about that
3) Get that tune-up done
4) Adress your low fuel pressure as possibility for running issues.
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