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Old 09-11-2012, 02:27 PM   #1
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Occasional High Idle

Awhile ago I made the mistake of getting the Firestone fuel system cleaner special. Messed up my engine for a long time. Very high idle and bad fuel mileage. Finally after replacing the TPS and IAC all was well. That was a couple of years ago and now I've started having a slightly high idle problem but not the same as before.

It will idle fine at about 600 when parked or starting it up but when driving and then stopping at a light or stop sign it idles at about 1100. A very light tap of the gas pedal will bring it back down to 600 and all is fine until the next stop. Sometimes it's fine but more often than not recently it will idle high. Engine is the 4.0.

Any thoughts?

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Old 09-11-2012, 03:54 PM   #2
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mine does the same thing but i haven't figured it out yet.....if i do, i'll let you know

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Old 09-12-2012, 08:14 AM   #3
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Surely someone has some kind of idea what the problem may be.
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Old 09-12-2012, 04:29 PM   #4
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Try cleaning out the IAC housing again? Might just be a little schmutz in there.
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Old 09-12-2012, 06:15 PM   #5
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Mine does the same thing. I can drive it to work and sometimes when I put it in park, it idles high until I tap the pedal then all is well. No clue why, would love to know!
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Old 09-13-2012, 08:35 AM   #6
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Quote:
Originally Posted by RubiCobra View Post
Try cleaning out the IAC housing again? Might just be a little schmutz in there.
I'll try that this weekend, maybe clean up the throttle body as well.
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Old 09-13-2012, 09:18 AM   #7
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I would suspect the tps again. I have a very similar story. About two years ago I had crazy idle issues replaced the tps and all was fine. Then about a week ago it came back but kind of different. When I went to unplug the tps it fell into pieces in my hands. GRRRR advanced auto crap...

So I would not eliminate tps as a key issue.
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Old 09-13-2012, 12:50 PM   #8
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Yeah could be the tps... Mine had a weird high idle after taking my foot off the throttle and engaging the clutch, like a red light. Turned out to be dirty IAC. If it were me I would clean up the TB and IAC first and then move to the TPS if the cleaning didn't fix it.
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Old 09-13-2012, 02:05 PM   #9
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Good to know I'm not the only one with that issue...at least AutoZone has a lifetime warranty on the TPS...
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Old 09-20-2012, 08:07 AM   #10
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I finally got it fixed last night after dealing with increasing problems since the weekend. Here is what i did to try to fix this slight high idle.

1. Took the throttle body off the engine, removed the IAC, the TPS and the vacuum thing I don't know what it does. I gave the TB a good cleaning with carb cleaner and a dab of oil near the spring where it was squeaking. Reassembled all and test drove it that Saturday afternoon. Ran fine, thought it was fixed. Didn't drive on Sunday. Monday it was worse than it originally was. Would idle at about 1000 or a little higher when coming to a stop and a gentle tap of the gas wouldn't stop it. I had to really stomp the accelerator to make it idle back down to normal. A few years ago when it did something similar I replaced both the IAC and TPS and problem was solved so I knew (hoped) that one of them was the problem again this time.

2. Ordered a new IAC online on Monday and it was there when I went home for lunch on Wed. Decided I had a few minutes so I threw it on and it was even worse. Started it up and it went up to 2000 rpms right away. I stabbed the throttle and now it was revving at 3000! Panic, shut down engine. Start it back up revs at about 2500 so I leave it and it slooooowwwwly goes down to about 800 on its own. Drive it back to work and it is constantly revving at 2000 at each stop. Stab of the gas and it sometimes drops.

3. Went to NAPA and picked up a TPS yesterday and installed when I got home. It is idling fine now but i've only driven it about 5 miles. Hopefully this fixes as I really don't want to spend too much on it before I sell it.

I just find it strange that doing those things not related to the TPS made it worse. Cleaning made it worse, new IAC made it worse.
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Old 09-20-2012, 11:18 PM   #11
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Originally Posted by SouthTJ View Post
I finally got it fixed last night after dealing with increasing problems since the weekend. Here is what i did to try to fix this slight high idle.

1. Took the throttle body off the engine, removed the IAC, the TPS and the vacuum thing I don't know what it does. I gave the TB a good cleaning with carb cleaner and a dab of oil near the spring where it was squeaking. Reassembled all and test drove it that Saturday afternoon. Ran fine, thought it was fixed. Didn't drive on Sunday. Monday it was worse than it originally was. Would idle at about 1000 or a little higher when coming to a stop and a gentle tap of the gas wouldn't stop it. I had to really stomp the accelerator to make it idle back down to normal. A few years ago when it did something similar I replaced both the IAC and TPS and problem was solved so I knew (hoped) that one of them was the problem again this time.

2. Ordered a new IAC online on Monday and it was there when I went home for lunch on Wed. Decided I had a few minutes so I threw it on and it was even worse. Started it up and it went up to 2000 rpms right away. I stabbed the throttle and now it was revving at 3000! Panic, shut down engine. Start it back up revs at about 2500 so I leave it and it slooooowwwwly goes down to about 800 on its own. Drive it back to work and it is constantly revving at 2000 at each stop. Stab of the gas and it sometimes drops.

3. Went to NAPA and picked up a TPS yesterday and installed when I got home. It is idling fine now but i've only driven it about 5 miles. Hopefully this fixes as I really don't want to spend too much on it before I sell it.

I just find it strange that doing those things not related to the TPS made it worse. Cleaning made it worse, new IAC made it worse.
I just replaced my IAC for the third time in 3-4 years. Not sure which IAC you bought but the one I bought from Autozone has instructions that tell you about the IAC needing to calibrate with the ECU. The new IAC I bought will indeed idle at 2000-2200 rpm right after you install it. The instructions say you have to drive it over 40 mph for the ECU to calibrate with the IAC. It will calibrate and idle normally if you do not have another problem. At least mine all have.

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