Rough idle - JeepForum.com

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post #1 of 16 Old 07-29-2012, 11:41 AM Thread Starter
MPM19
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Rough idle

I have a fuel injected 1995 jeep wrangler with a rough idle. Any suggestions to smooth it out.
I have changed the spark plugs, wires, distributed cap and cleaned the throttle body.
I was thinking of changing the timing but can't find a solution to do so with the fuel injected engine. Any suggestions?
It's a 4 cyl

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post #2 of 16 Old 07-29-2012, 03:31 PM
mholmes7979
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Check the air fittings to the fuel rail. Also check the other end around the carb. My 1994 4.0L would run ruff at idle and want to stall. Changed both air fittings & now it's good.
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post #3 of 16 Old 07-29-2012, 05:23 PM
pete1991YJ
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Does it happen when its warm or when its cold? All the time? It does make a difference - the computer does not listen to the O2 sensor until the engine is completely warmed up. If it starts running rough then, its a pretty good sign.

Other things to look for would be an exhaust leak - you would be surprised how many manifolds work loose especially at the back.

Ditto for vacuum leaks - spray around the ends of all hoses with some carb cleaner and listen for the idle to change - that would be a leak.

The timing is completely not adjustable on these - the computer does it all based on the sensors.

BTW can you read the computer codes? Its easy and free, all you need is the ignition key. Here's a video that shows how:

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post #4 of 16 Old 07-29-2012, 05:50 PM Thread Starter
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It will idle rough at all temps. It drives great though I fixed an exhaust leak last week and it helped a little.
It is a kind of a pulsing rough idle.
Is there a way to adjust the idle ?
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post #5 of 16 Old 07-29-2012, 06:56 PM Thread Starter
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I got 12, 33, and of coarse 55.
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post #6 of 16 Old 07-29-2012, 07:07 PM
animal0307
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I believe those are battery unhooked, AC clutch relay and end of code. They are all normal for most of us.

I second checking for vacuum leaks. I've heard to use a propane torch that has been cracked on but not lite for checking for leaks. Just wave it around the lines and listen for it to change.

What exhaust leak did you fix and how?
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post #7 of 16 Old 07-29-2012, 07:58 PM Thread Starter
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Where the manifold meets the pipe kind if where the passenger sits, the bolt threads were stripped and a lot was getting out. I fixed it for the leak but mostly because of the squeaking noise it would make!!!
I put new hardware in, exhaust cement and cranked it down.
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post #8 of 16 Old 07-31-2012, 12:53 PM Thread Starter
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Hey guys
I removed all of the fuel injectors cleaned them and put new o rings on.
It still idles rough so I don't know what it could be. It has 144,000 miles so I guess I'll just have I deal with it.
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post #9 of 16 Old 07-31-2012, 07:34 PM
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I just bought a 91 and was reading this forum to learn the world of the YJ. My new YJ also has a rough idle and I planned to clean the throttle body. Did you also remove the IAC take it apart and clean the plunger? I'm doing that this weekend. However I have more than a few exhaust leaks to repair on this thing which is getting the hot end of my welder next weekend.


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post #10 of 16 Old 08-01-2012, 04:17 PM
mholmes7979
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Not trying to get you doing more than required but, compression, inspect plugs, wires , rotor & cap. After that injector cleaner and air leaks. If all this don't do it ?
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post #11 of 16 Old 08-01-2012, 04:58 PM
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I agree with the previous poster, check the iac (idle air control) motor. they also might call it an idle speed motor. when your throttle plate is closed, i.e. foot off gas, this motor is what allows air into the engine. the computer controls the idle by opening the plunger to various depths to allow air in. It is the idle control system on your Jeep. One key factor pointing to this being a problem is the jeep running okay at speed. it will run okay while your foot is on the gas, and run bad at stops. You can't really test it, but they aren't the most expensive thing to replace. we replace these motors at the shop i work at, all the time. Not just on Jeeps, but all cars, even the newer 2000's and up. They get dirty and "slow".
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post #12 of 16 Old 08-01-2012, 05:32 PM
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I've never replaced an IAC. All I've done is take them apart and. Lean all the gunk off the plunger. This works great everytime.


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post #13 of 16 Old 08-01-2012, 06:58 PM Thread Starter
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I just cleaned the IAC and entire throttle body but nothing really changed although the piece was pretty dirty.
I'll probably try a compression test
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post #14 of 16 Old 08-01-2012, 07:18 PM
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Hmmm. Okay. Idle = air fuel and spark all firing in the right time. Air is good. Fuel is good. Spark is good. Time cannot be a problem. I'm voting spark. Something spark.


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post #15 of 16 Old 08-01-2012, 08:46 PM
deathtrap
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compression test/ cyl. leak test. bet you got a leaky or burnt valve. mine did.
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