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Old 10-02-2012, 06:46 AM
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engine idle rev

I've been doing some searching before posting and can't seem to find this topic anywhere. This problem has been driving me nuts lately and can't seem to figure it out. Don't have a reputable mechanic in the area either so either I fix it or get screwed one way or another.

I have an 02 4.7 WJ and when in park or nuetral the engine will rev on its own from 500 RPM up as far as 3500 RPM and continue to do so until I start to drive. Of course if I don't time putting it into gear correctly I jolt forward and I know its doing a number on the tranny. Also randomly if I'm at a stop light the engine trys to rev again and will stall if I hold the brake down hard enough. I'm afraid one dayI'm going to rear-end the guy in front of me. I've check for a vacuum leak and can't seem to find one. Any ideas why i am experiencing this?

I'm going to try and take a video with my phone today at coffee break and post up so you can see what I'm talking about. Thanks in advance for any help
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Old 10-02-2012, 07:15 AM
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Re: engine idle rev

I had similiar problems and changed the tps sensor. That solved my issue and a few others.
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Old 10-02-2012, 07:28 AM
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Re: engine idle rev

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Originally Posted by Thumper828 View Post
I had similiar problems and changed the tps sensor. That solved my issue and a few others.
Do they go bad? Do you think if there is an exhaust leak it would cause this problem? Co-worker just told me there could be a crack near an O2 sensor to make this happen. I checked quickly but didn't notice one.
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Old 10-02-2012, 07:32 AM
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Re: engine idle rev

The TPS will make the idle do strange things. They are a common problem on the WJs. I suggest picking up a new Mopar piece to install then reset the computer.
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Old 10-02-2012, 07:36 AM
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Re: engine idle rev

I will try that out this weekend and report back with an update.
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Old 10-02-2012, 08:07 AM
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Re: engine idle rev

If you have a scanner which shows live data, you can see the TPS position in % and you probably see it fluctuating. Mine stays around 12% in idle and it should be steady. The TPS is well known to give problems like this and can also cause shifting problems when becoming bad. easy to change, just one quick disconnect connector and 2 torqueX screws. You even donīt have to remove the airbox.
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Old 10-02-2012, 08:34 AM
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Re: engine idle rev

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Originally Posted by Frango100 View Post
If you have a scanner which shows live data, you can see the TPS position in % and you probably see it fluctuating. Mine stays around 12% in idle and it should be steady. The TPS is well known to give problems like this and can also cause shifting problems when becoming bad. easy to change, just one quick disconnect connector and 2 torqueX screws. You even donīt have to remove the airbox.
Thats good news. Hopefully it is just this simple fix.
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Old 10-14-2012, 12:28 PM
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Re: engine idle rev

It's been a week now since I installed a new TPS sensor. Ended up picking one up from Autozone for $34. It's a Duralast brand seems to work fine. Disconnected the negative terminal of the battery installed the new sensor with a torx bit and fired her back up. No more revving and it only took about 10 minutes. Glad I checked here before sending her in to the shop. I was quoted over $2k from two different shops in town and it turns out to be a simple 34 dollar fix.

Thanks again guys for all the help...
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