Sticking idle - JeepForum.com

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post #1 of 17 Old 09-18-2011, 06:30 PM Thread Starter
Dabbill
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Sticking idle

Went wheeling yesterday nothing to bad other then bending stock control arm. Buddy gave me one and we swapped it out. Drove the jeep home with no issues. This morning i drove the jeep and it seems the idle is sticking at high idle around 1200 - 1500rpm. When letting off the gas in gear it doesn't want to drop below 3000rpm on a hill that normally will drop to around 1200rpm. I pulled the TB and cleaned it really well. Replaced the TPS, and cleaned the IAC. Couldn't find any vacuum leaks. Any other ideas i am stumped.

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post #2 of 17 Old 09-18-2011, 07:05 PM
flying_bosun
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Don't know if it's related, but I've been having some idle issues lately after disengaging 4x or the lockers (not sure which triggers it yet) and for now disco'ing the battery for a couple of minutes resolves the issue. I'm looking into it and it may be related to needing a flash because of a recent OPDA swap, but I'd try disco'ing and go from there.

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post #3 of 17 Old 09-18-2011, 07:44 PM
Jerry Bransford
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A high idle is caused by either a vacuum leak or a dirty IAC (idle air controller). The IAC is what controls the idle and provides all of the engine's air when your foot is off the gas. There are a lot of threads in JF on how to clean your IAC with throttle body cleaner, look for a possible vacuum leak as well.

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post #4 of 17 Old 09-18-2011, 07:46 PM Thread Starter
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I used half a can of TB cleaner just on the IAC, and the other on the TB. Cant find a vacuum leak any where, so i am guessing the IAC just needs to be replaced.
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post #5 of 17 Old 09-18-2011, 07:51 PM
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I'd try a few more tries at finding a vacuum leak or other problem, the IAC doesn't have a reputation for failing. Did you remember to clean the throttle body's oriface the IAC's plunger fits into?

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post #6 of 17 Old 09-18-2011, 07:53 PM Thread Starter
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I have a 05 so it doesn't have a plunger on the IAC. Also i cant seem to even find the IAC on a parts store website.
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post #7 of 17 Old 09-18-2011, 08:06 PM
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It still has a plunger that fits into a hole into an oriface in the throttle body, it's just a larger diameter plunger than was on older model IACs. Did you clean the surface inside the oriface that its solenoid actuated plunger fits into?


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post #8 of 17 Old 09-18-2011, 08:08 PM Thread Starter
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I cleaned every surface i could get to with the can of spray. I didnt want to move anything in the IAC but i sprayed a bunch of cleaner in it.
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post #9 of 17 Old 09-18-2011, 08:11 PM
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If you didn't also clean what the IAC plunger seats into, the oriface in the throttle body, there's a chance it is allowing air to leak past the o-ring which can jack up the rpms.

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post #10 of 17 Old 09-18-2011, 08:12 PM Thread Starter
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I meant i cleaned every surface on the IAC and the TB inside and out.
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post #11 of 17 Old 09-20-2011, 12:49 PM Thread Starter
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Took the IAC off again and used some more cleaner on it. Still the same. Sprayed starting fluid around the intake, no change in idle.

It idles just fine, its not rough or anything like that, no delay in coming off idle. Had auto zone try to pull codes from the ECU, came back with nothing. I don't know what else to check, its almost like driving an auto right now, you let off the gas and it doesn't want to slow down like normal. I guess you couldn't say its sticking coming back to idle, but it takes much longer then it should to return to idle when you take your foot off the gas.
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post #12 of 17 Old 09-20-2011, 10:52 PM
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Butterfly valve plate returns normally? If that's ok and the IAC is ok, I'd spend some more time looking for a vacuum leak. Maybe a bad TPS but it sounds more like a vacuum leak if the valve plate is closing properly and the TPS is ok.

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post #13 of 17 Old 09-21-2011, 03:51 AM Thread Starter
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TPS is the first thing i replaced. Butterfly plate is tight and has lots of spring tension. Maybe air flow sensor not reading right? Not sure where or how to look for a vacuum leak any where. I sprayed some starter fluid around the TB with it running and the idle didnt change at all.
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post #14 of 17 Old 09-21-2011, 04:07 AM
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Does your heater fan vent selector work. Is it slow? This vac line is often the point of a vac leak.
Also spray around the block where the intake meets at each cylinder.


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post #15 of 17 Old 09-21-2011, 07:25 PM Thread Starter
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I took off that line you have in the picture, my idle increased, put it back on and my idle went back to normal. So guessing that is not the leak. Engine was to hot to try and move stuff around to spray the intake. Lots of stuff in a small area lol.
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