Every once in a while, maybe once a week my engine will suddenly rev from normal to about 1500 rpm and back to normal - 1500 again repeats this a few times when I am sitting a stoplight or parked. Not particularly dangerous if in park but can freak you out a little at a stoplight parked 2 feet behind someone and you have to jam down on the break....

Anyone ever have this problem or any ideas? Its the V6 engine, no mods or anything.

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2002 Liberty Sport All Stock for now.

That sounds like maybe a vacuum leak. ECM detects it and revs the engine to overcome the leak.... just a suggestion.

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'99 Tahoe, 3" BL, 285/75/16's , MT II's.
'05 Liberty Sport, -wifey's
'98 Poncho Fireturd, 3.8L, .....the purple pig!

check to make sure the carpet is hooked on the floor hook -

There have been some runaway Liberties from carpet catching the gas pedal.

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2005 CRD
stuff
Skeptic quod gratis asseritur, gratis negatur

I would check to see if you have any error codes. This will give you a good idea of what's going on.
Vacuum leak or a failing Throttle Position Sensor would be my guess.

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Take the road less traveled.

I agree re vacuum leak. That being said, my throttle plate was carboned up and was sticking. SO when at stoplight it was at 1100 and really had to apply the brakes. I used carb cleaner on shop towel cleaned inside the throttle body and then moved plate to open position. Used q-tips with carb cleaner to get both edges of the plate clean. Then applied trumpet oil to edge of plate and rpm was now not sticking up.