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Engine revs up automatically

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Old 07 Feb 2011, 02:35 pm
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Join Date: Oct 2010
Location: Travel between Belgium and USA
Posts: 265
Question Engine revs up automatically

When I'm driving with the AC on (manual transmission), and get into neutral while rolling to the next stoplight, the engine goes below 1000rpm, revs up to 2000rpm, slows down to 1000rpm then revs up to 2000rpm again, and continues the process until I'm slower than 20mph. When the car is stationary, the engine does not rev up, and stays between 800 and 1000rpm.

I also noticed that the least pressure I up on the gas pedal, the tachometer jumps between 2000rpm and 2.200rpm. It seems that I can not get the tachometer to 1500rpm without putting the car in gear.

Is there something wrong with my car?

I've also noted that when I'm driving in gear, and the engine reaches 2500rpm, the traction is way lower, almost as if I release the gas pedal half way.
It accelerates normally upto about 2,2k rpm, has a dip around 2,5k, and seemingly accelerates normally (or stronger) again after 2,8k rpm.

Last edited by ProDigit; 07 Feb 2011 at 02:41 pm.
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Old 07 Feb 2011, 03:24 pm
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Join Date: Sep 2001
Posts: 27,749
Default Re: Engine revs up automatically

As far as the second part of your question, all PT's have a bog/lag right after taking off from a standing start. A lot of us took care of that by adding a free flowing air filter which took care of most of it. At about 2800 - 3200 the PT reaches it's "power band" (where it makes most of it's power) and that why you feel the stronger surge of power.

The up and down revs could be caused by a dirty or inoperative IAC (Idle Air Controller). The black gizmo attached to the back side of the throttle body. It can be taken off pretty easy and cleaned or just replaced.
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Old 07 Feb 2011, 07:09 pm
Obsessed Cruiser
Join Date: Nov 2007
Location: Mooresville, NC
Posts: 5,324
Default Re: Engine revs up automatically

I'm gonna have to search for the info on this one. I had a friend with a similar issue, the surge ONLY occurred with the AC turned on cold air. We found one of the units in the AC system had a clog building... man I don't remember which one and can't find the info. I've got it here somewhere on an old hard drive, gonna have to go search.... something we disassembled and cleaned out and put back together and it worked find after that....
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