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Old 03-16-2017, 09:20 AM
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Jeep 5.2L rough idle problem

I have a 95 ZJ with a 5.2L engine, it has 180k miles on it, auto trans. I've had for almost a year and right at Christmas it got a rough low idle and began stalling out when coming to a stop or revving high and letting off the gas. I haven't done anything except for a transmission fluid change and a new fuel filter. The check engine light is on , the codes are 12, 52, 21, 21. Any ideas as to what it might be? I've read about IAC Valve going bad, or having a vacuum leak. Any help is greatly appreciated!

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Old 03-31-2017, 10:45 PM
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Re: Jeep 5.2L rough idle problem

codes from my understanding are:

12 - Battery recently disconnected
21 - Oxygen sensor/faulty wiring
52 - Oxygen sensor detects Rich mixture

I would check into the obvious codes for the Oxygen sensors but I would also check the IAC and clean it along with the Throttle body. Also check all grounds and clean them. Codes are saying Rich mixture, so maybe time to look into the Spark plugs and seeing how they look. This will hopefully help get you started.
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