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Old 03-01-2014, 06:23 PM   #1
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Question 89 wrangler rough idel after driving.

Ok people first time posting on the forum. My jeep (89 jeep wrangler 258 manual) starts up fine and idles good with a few pops hear and there but after running it down the road at normal speeds it idles rough shakes and pops at a stop. this will last for 3 to 5 minutes and then clears up. started to happen when it got cold out but never did it the past 12 years I've owned the jeep. Since the problem started I have done the following. fuel pressure is set to 3.5 psi on my weber 32/36. Nutter bypass is done. new EGR. ported vacuum. new vacuum lines and brake booster. Plugs and wires with only about 5,000 miles on them so I did not change. no leaks on carb or intake.

On a interesting note I set my timing with a vacuum gauge for the first time to get the best vacuum, the jeep runs a lot better but if you hit it with a timing light its running at about 20 instead of the recommended 8 after the nutter.

After all this the jeep runs allot better but I still have the same problem with the idle. Any one have any advice?

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Old 03-01-2014, 09:36 PM   #2
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Welcome to the forums. Check your plug wires and spark plugs. Maybe one cylinder is missing when it's cold or at idle? I had a short in my #6 wire. I don't know much about the carb'd 4.2 Will your's throw any check engine light?

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Old 03-02-2014, 01:20 PM   #3
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thanks for the reply. I've never seen the check engine light on my jeep in over 12 years so I'm not even sure it works. as for the plugs i will check them over thank you.
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Old 03-02-2014, 01:33 PM   #4
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I have an 88 wrangler and mine was doing something simular.It turned out that the fuel filter in the tank was restricted.Parts houses told me that it didnt have one in the tank,but I was out of ideas so I checked it out.It worked for me.Good luck.
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Old 03-02-2014, 01:35 PM   #5
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rough idle

There may be a filter in the gas tank.There was in my 88 wrangler though the parts houses said there wasnt one.
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Old 03-02-2014, 02:59 PM   #6
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Carbed you might have one in the tank. Check the Haynes manual.
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87 yj, 4.0, small lift, 33s, slowly taking jeep-roids
75 cj5 304, Fiberglassed, 4:56, lifted, 35s
79 cj5 built 401
73 cj5 plow jeep.
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Old 03-02-2014, 03:10 PM   #7
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Thanks I will check that out since the plugs and coils look fine. But I have another question. What is the round thing connected to the ignition coil bracket with a black wire that connects into the second yellow wire on the top of the ignition coil? The black wire appears to have broken off that thing. Is it just a ground and if so do I need the round cap thing or can I just wire it to the bracket? From what I can tell the ignition system is all stock bye the way.
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Old 03-03-2014, 06:47 AM   #8
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Thats your condenor wire.You need that.
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Old 03-03-2014, 04:12 PM   #9
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I think you may be talking about the noise suppressor for the radio.
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Old 03-03-2014, 06:25 PM   #10
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If you still have an Ignition Control Module on it, which you most likely do even though you did the bypass, it could be going bad and you're losing spark. Or, you can also have too much moisture in your fuel. A stock carb'd 89 4.2 doesn't have an in tank fuel filter. It just has a mesh screen that fits over the pick-up on the sending unit. It's possible that it can be causing not enough fuel to flow, but I wouldn't drop the tank yet without checking electrical components such as the ICM, coil and wires. If you had an original carb'd 4.2 the fuel filter would be in front of the carb directly connected to the fuel line. Make sure there isn't some type of filter someplace else. You can also have a problem with the carb. Unfortunately, there are a lot of things that can cause this problem. Your 89 4.2 doesn't throw codes so you have to diagnose it old school.
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Old 03-03-2014, 10:30 PM   #11
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Is there a spot to hook up a fuel pressure gauge and check that coming from the tank? At least that would rule out that half the equation. But again, like kik said, wires and check plugs too. Get a spark checker. Works wonders.
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87 yj, 4.0, small lift, 33s, slowly taking jeep-roids
75 cj5 304, Fiberglassed, 4:56, lifted, 35s
79 cj5 built 401
73 cj5 plow jeep.
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Old 03-05-2014, 08:17 AM   #12
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Ok after a new distributor and some fine tuning of the timing the rough idle after driving is gone. At regular idle after she sits awhile she runs well with a miss every now and then nothing like before. I'm still concerned about the timing being so high compared to the recommended 8 degrees mine still gets the best vacuum and runs the best around 22, 24 at about 650 700 rpms. Also after correctly installing the new distributor it is in a completely different angle then previous. So I guess I'm getting somewhere. Thanks for the help so far.

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