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Old 01-25-2012, 01:36 PM   #1
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Rough Idle Help?

My 1997 4 cylinder Jeep wrangler has had a really rough/shaky idle since the day I bought her. When in idle at a stop light she shakes and her rpms go from 1500 up to 1800 and sometimes down to like 1300 rpms. She drives great and no major problems other wise but the shake is driving me crazy. I just feel like it's hurting my Jeep so I was wondering what I could do to possibly fix the idle?

I have no check engine light on or anything, I've replaced the spark plugs, both o2 sensors, change the oil every 2,500 miles, always keep her full of gas and take pretty good care of her.

Any help/ideas on what I could do to cure the idle? Thanks!
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Old 01-25-2012, 02:05 PM   #2
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Old 01-25-2012, 03:16 PM   #3
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Look the engine over for a vacuum leak. There's gotta be some 15 year old cracked hoses somewhere.

Try some fuel injector cleaner.
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Old 01-26-2012, 10:57 AM   #4
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Thanks everyone so far! That link was super helpful! So today I went out and was going to start cleaning everything when I noticed the thing on top (sorry don't know technical terms doing the best I can) was broken. It looks like it had been taped but now the tape has ripped and its open. Its the large thing that attaches to the air filter. Do you think that could have any effect on the rough idle? Thanks!

Pic:
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Old 01-26-2012, 12:19 PM   #5
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Mine doesn't run any different with the air box on or off, all the sensors are on the throttle body nothing in the tubes.
Now that crack will suck in dirty unfiltered air witch isn't good for your engine
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Old 01-27-2012, 07:24 AM   #6
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Alright official news! My boyfriend (automotive student) took it to school that night to be all tuned up, clean the IAC, Fuel Injectors, run some tests on it and fix that nasty crack in the image above. He said that the IAC had a broken bolt and was held together with wire (yay! used cars! haha) and that it wasn't working properly.

Then hooking my jeep up to some machine that he says can control the IAC he said didn't work because it's broken so I'm going to have to replace it. Also now my check engine light is on for my IAC (I don't have the code on hand I can get it later).

The Jeep sounds much better and he said I'll start to get better gas mileage (bonus!) Now it just idle higher rpms. But the shaking is not completely gone yet, hopefully when I replace the IAC it will stop So when I go to the auto store he told me to pick up these things:
IAC
Distributor Cap
Spark Plus (again)
and Rotor
He said he can fix it on Sunday so hopefully I will have good news for all of you!
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Old 01-28-2012, 05:02 PM   #7
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im new to the wrangler area first time owning one just pick up a 87 wrangler 2.5 five speed eight in lift on 35 in boggers and my problem is when i get in it to turn the key to start it the rpms go from o to 3000 then slow climbs down to a thousand and it idles there and i was driveing it last night and when i was driveing it stalled on me like foot was in the gas and was not moveing then i pull over down shift to second gear was just stalling still then died and now it wont turn over what do u guys think it could be want to keep it cause i pick it up for 900 bucks and hope its a cheap easy fix
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Old 01-28-2012, 05:48 PM   #8
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A fluctuating/bad idle is very often caused by a bad TPS (throttle position sensor). The TPS gets dirty inside and when it does, it sends an erratic signal (voltage) to the engine computer which can cause a bad idle and erratic acceleration as well. The TPS is what tells the engine computer how far you're stepping down on the accelerator pedal so it can cause all kinds of strange issues.

Unfortunately, the TPS cannot be cleaned, it can only be replaced. Fortunately, they are not expensive.

My previous TJ had a really bad idle and erratic acceleration and replacing the TPS fixed it. Replacing it takes no more than ten minutes, it is a one-banana job.
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Old 01-30-2012, 12:38 PM   #9
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thank u well try it and get back to ya
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Old 03-19-2013, 07:33 PM   #10
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I am having the same problem except my idle drops to about 600 rpms when stopped. I have replaced TPS. MAP. Canister Valve Silenoid, Both O2 sensors, cap, rotor, wires and plugs. Oh and the battery. What else can I try?
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Old 06-28-2013, 11:43 PM   #11
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Wranglers normally idle between 600 and 750 rpm if your idle is rough though it could be due to numerous things including worn engine mounts, bad air/fuel ratio, or even just age. My 95 has problems at the moment but normally idles at 750 and has a pretty good rumble due to shot engine mounts and age. Good luck.

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