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Old 09-15-2011, 02:41 PM   #1
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Inconsistent Idle

My jeep's idle has been very weird lately. It will go up and down from 800 to 2,000 rpms randomly. Even if I'm sitting still at a stop light.

Sometimes when I push the clutch in it will stay at around 2,000 rpms and I can give a little throttle and it will go back down to the normal 7 - 800rpms.

Any advice on what could be causing this?

Thanks

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Old 09-15-2011, 03:20 PM   #2
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Try running seafoam thru your vacuum line into your intake manifold. You may have some gum/varnish/carbon junk built up. If you do this the right way and a lot of white smoke comes out, then thats what it was. Seafoam is designed to improve idling and a lot of other mechanical issues. Also, bring it into a local shop for a free diagnostic. (most will tell you whats wrong with your vehicle before you proceed). Hope that helps.

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Old 09-15-2011, 03:24 PM   #3
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Old 09-22-2011, 02:39 PM   #4
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Thanks for the advice, how much of the seafoam do I need to run through my lines?
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Old 09-22-2011, 02:46 PM   #5
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Forget seafoam...clean your throttle body. It's cheap, easy, and makes a big difference.
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Old 09-22-2011, 02:53 PM   #6
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There is a very good possibility it is your idle air control valve. Surging idle is the predominant symptom.

I used to clean the one on my ZJ about every 20K miles. Just pulled the valve, cleaned the sensor and the housing with brake fluid (FSM recommended cleaner) and replaced.

I don't know if there are any write ups here... over on JF there is a good write up, see post # 10277503 or search "cleaning IAC throttle body"
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Old 09-22-2011, 08:03 PM   #7
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I'm betting either a dirty TPS (which cannot be cleaned) or a dirty IAC (which can be cleaned.
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Old 09-22-2011, 10:44 PM   #8
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IAC most likely. Also while you are cleaning it, open up the butterfly on the throttle body, and look for a ring of deposits under it. Those also can block the butterfly from closing properly and the idle will kick up, as the tps is telling the computer you have your foot partially on the throttle, so it in increases the fuel flow from the injectors.

Blip the throttle and it can sometimes seat again and all works as intended, until it hangs up again.



The Seafoam bit through a vacuum line is good for cleaning out the intake and valves, but does nothing for the IAC or butterfly build up. Some Seafoam in the fuel tank though will help with keeping the injectors cleaned up.
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Old 09-22-2011, 10:50 PM   #9
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Personally, I don't believe any fuel injector cleaning additives are needed to keep the injectors clean like was needed until the mid-seventies. That is when the gasoline manufacturers finally caught on and all started including enough fuel injector cleaning additives in their gasolines, even in their low (87) octane grades. It wasn't long after pretty much all engines had gone to fuel injection that the gasoline manufacturers were coerced to finally include enough cleaning additives which they all did.

I used to have a bunch of Jeep and truck dealerships as customers and I made it a point to ask all the mechanics how many clogged/dirty fuel injectors they had ever seen. The old mechanics said it had been years since they had seen one and none of the younger mechanics had ever seen one.

Which doesn't quite back up car dealerships pushing those $99 fuel injector cleaning "specials" so hard and telling everyone how important they are.
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Old 09-29-2011, 09:44 PM   #10
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Thanks guys! I cleaned the IAC and its back to normal.

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