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Engine light is on,rough idle


 
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GREATONES96
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Joined: 28 Jul 2005
Location: ARIZONA

PostPosted: Sun Apr 08, 2007 4:30 pm    Post subject: Engine light is on,rough idle Reply with quote

My jeep started running rought the other day at idle,day later the light came on and i went into checker auto and they hooked up the computer and it said mis spark in cylinder one,I went home and check the wire the plug and cap and rotor and everything looks fine, When i start to drive it seems to be fine unless i am at idle.then you can feel the miss spark.I took the wire off the cap and could still see spark also from the plug and could see spark,Could it be a injector? OPPS sorry it is a 97 xj 4.0 with 186.000 miles and had new cap and rotor an wires and plugs 6 months ago.. thank you for antones help in this matter, very frustrating. shawn
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Mon Apr 09, 2007 7:16 am    Post subject: Reply with quote

What did you install for wires? The only wires I will buy are OEM because I've had too many issues with aftermarket ones. You could swap the next closest plug/wire with it to see if it moves but that means another trip to the parts store to check the codes. I got fed up with going this route and bought a Scanguage, it's paid for itself multiple times.
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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GREATONES96
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Joined: 28 Jul 2005
Location: ARIZONA

PostPosted: Wed Apr 11, 2007 7:33 pm    Post subject: Reply with quote

ok i wnet and bought oe plugs wires,plugs and cap and rotor and no change it does the exact same thing,,,,could it be a fuel pump? i took the plug wires off one at a time while running and it acted as if it was missing with all cylinders. unplugged the fuel injector one at a time and did the same thing which makes me believe it is something else,whta happens when your fuel pump starts to go or oxygen sensor,,,,it idles like it is missing but while driving 45mph it feels fine......man this is frustrating...
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Brad The Best
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Joined: 14 Jan 2007
Location: Kamloops B.C Canada

PostPosted: Wed Apr 11, 2007 8:25 pm    Post subject: Reply with quote

any excessive noise from your pump ? i would say you have to check the pressure on the fuel rail to be sure . still sounds like it would be a bad injector if you have good spark .

does your jeep miss at idle or just idle ruff , if it idles ruff i would probably clean your throttle body and iac .

those little computers aren't always right .

02 would probably affect you more all around .

when was the last time you changed your o2 sensor , if its something silly like factory then go change it .

p.s i hope you didn't unplug injectors while it was running they can pack enough of a punch to kill .
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GREATONES96
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Joined: 28 Jul 2005
Location: ARIZONA

PostPosted: Wed Apr 11, 2007 8:58 pm    Post subject: Reply with quote

IT feels like it is missing,i just cleaned the throttle body what is the iac? And how do you find out if it is a bad injector? Thank you for your response and help so far.....
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Fri Apr 13, 2007 5:52 am    Post subject: Reply with quote

IAC means IDLE AIR CONTROL VALVE. You can find info on it on the web or check a repair manual. In a quick search I found this which may be close enough: http://en.allexperts.com/q/Jeep-785/Jeep-Stalls-idle.htm
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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JeepinNH
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Joined: 13 Sep 2005
Location: New Hampshire

PostPosted: Sun Apr 15, 2007 7:38 am    Post subject: just another thought Reply with quote

I was thinking, when my upper O2 sensor failed it really messed up how the motor ran. I had a misfire code at one point. You can unplug the sensor and see how the car runs, this is how I figured out my issue was the O2 sensor because I never got a code dor it. When unplugged, the computer will use a default setting for the air/fuel mixture. Doing this will throw a code but at least you can discount it if the issue is still there.
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Mike

Present: 99 Cherokee
Past: 86, 87 Cherokee; 94 Grand Cherokee
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Brad The Best
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Joined: 14 Jan 2007
Location: Kamloops B.C Canada

PostPosted: Sun Apr 15, 2007 7:22 pm    Post subject: Reply with quote

you could swap injector's . the IAC is a sensor on your throttle body the part you care about is the little nipple sticking out inside the throttle body .

to see if a cylinder isn't working just read the temperature of it with ... well i use an infer red gun so im not sure what you can use .

you could try getting your injectors cleaned or replace them .

what voltage are you reading on your dash with the vehicle running ? a low voltage can mess with the reference signals (just ruling it out) you want around 14V

are you plugs gapped properly ?

what cylinder do you think isn't working
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