89 YJ 4.2L idle is rough, need your ideas :) - Jeep Wrangler Forum

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Old 03-29-2010, 08:45 PM   #1
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89 YJ 4.2L idle is rough, need your ideas :)

Hope you fella YJ'rs with the 4.2L can help me on this one. I have basically done all the tune up things I can do to it since owning it for about a year 1/2 now.
New plugs, adjusted timing, new oil filter, air filter, new battery, new PCV.

it runs good at rpm's above idle but at idle it's pretty rough. I've had difficulty turning the idle down with the adjustment screw so I am wondering if I need to rebuild the carb with new seals?


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Old 03-29-2010, 08:48 PM   #2
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Not a carb'd YJ guy but remembering back from my carb days I'd say gaskets or vacuum lines. Any air leak (vacuum leak) is going to give you grief.

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Old 03-29-2010, 09:36 PM   #3
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I've rebuilt an Edel 1406 twice on another Jeep and am here to tell you...let the pro's do it!
Could be PCV valve.
Fuel filter.
Dirty air filter.
Back to carb: filtyh carb that needs a good carb spraying. When I did take mine apart there was all sorts of gunk, but I can't swear it needed all the new gaskets. But a booger size ball of gunk is all it takes sometimes to unseat a rod.
You said timing, but is dist in good shape? Timing belt/cover can cause this too.

Some of these things are lucky ways out and some are expensive.

But the idle port screw (you have just one?) is sticky? Does it have a spring on it? Could be that simple, too. If the screw doesn't feel normal (and you would know best) maybe you should tear into carb a little.

Hope any of this helps.
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Old 04-21-2010, 07:09 AM   #4
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It's your carb

It's an air leak at the point where the throttle arm enters the carb body. You can test it by spraying carb cleaner at the point of entry - if the idle evens out or increases that proves theres a leak. There is no fix except to replace the carb. I've had my 89 for 150K miles. At about 75K I replaced my 1st carb - Im now having the symptoms again so time to replace.
Good luck
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Old 04-21-2010, 09:54 AM   #5
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ok this sounds like a simple clean the bowl out and make sure your passages are clean and you should be on your way. worked for me, any way lets atart a list. first get your self some cab spray with the little straw (it is needed). two go to walmart and find guitar strings. they come in many sizes and work great for cleaning out the passages inside the carb.
next find someplace were u can sit and take it apart while not being disturbed at all. and were you can get some air the fumes make you a little loopy.next take your time tearing it apart and make sure of were every screw nut spring and rod goes. once you have it apart clean and reassemble and let us know if it takes care of the problem .

hopes this helps you
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Old 04-21-2010, 10:49 AM   #6
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Run Seafoam through it.. Mind you mine would backfire on occasion before I did the treatment but blew no smoke, this is all crap coming out of my jeep. After about ten minutes it quit smoking and has ran smoother with no backfires since..
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Old 04-22-2010, 12:23 PM   #7
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check your smoke out the tailpipe while it is idling rough. If you have black smoke and it smells gassy, then you have a problem with spark or timing.

If you do not have black smoke at a rough idle and it does not smell gassy, then you have a restriction in your fuel system and/or an air leak.

At least this would narrow your focus...
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Old 04-23-2010, 12:38 AM   #8
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I agree with morphious. Our 4.2 idled like crap. These carbs are famous for plugging up. Really easy to rebuild. Rebuilt the carb and it would idle just fine. The next time we had an issue with the idle I found crap stuck in it again. Yes, also seafoam does not hurt. Glad I got turned on to it. All our vehicles get the treatment.
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Old 04-23-2010, 08:19 AM   #9
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i've had some trouble with mine as of late too... haven't noticed any black smoke but def a gassy smell... should i look into spark and timing? i wanna get this fixed soon
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Old 04-23-2010, 01:22 PM   #10
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check the vacuum line on the back of the intake manifold, near the firewall. mine has come undone before and i had the same symptoms as you. good luck.

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Old 04-25-2010, 03:48 PM   #11
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thanks checked the vacuum line and it seems to be okay
guessing i just need to take it in and have it checked out
someone said i should try a nutter bypass
has anyone done this and think it will help me out?

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4.2 , carb , carbuerator , idle

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