So I am on my way home from work last night, see the stop sign ahead let off the gas. I usually give myself plenty of coasting time instead of slamming on the brakes at the last minute. Look down at my speedometer and I'm not slowing down. The cruise is not on although it was, but I tapped the brake and shut that off or at least the light did and I still wasn't slowing down. I applied the brakes, stopped for the sign and the car took off again without hitting the gas. It seemed the idle wanted to control the car.

I decided to try and run a couple of test.

1. Slowed down and put the car in neutral - the idle started reving up. Not wanting to hurt the engine I placed it back into drive and slowed down again this time coming to a stop. Put the car in neutral and the idle started increasing again.

2 I shut off the engine and tried the same steps again and couldn't get it to duplicate the problem.

Any suggestions what may be causing the increasing idle?

 

My brother had his 2000 Grand Prix do the same thing and of course could never duplicate it for the mechanics at the shop. It ended up being a wiring problem that he paid to have fixed instead of looking at it himself. He's not really a mechanically inclined person so he let them take care of it.

 

Not sure what year car this is, but you might want to check the lines running to the throttle. Sometimes excessive gunk build up can cause the lines to stick, essentially keeping the throttle open while your foot is not on the gas. Check out all those lines (there should be a pulley like set up somewhere, thats where mine was sticking).

 

Oh sorry for the lack of details. 02 impals with 3.4L. I thought about the lines or a vac leak or something but I would think it would be repeatable if that were the case. But when I turned the car off it didn't repeat.

 

If there is gunk build up on the lines the problem may not be repeatable... when the engine heats up the gunk loosens, so you may only experience the issue when the engine is cold.

Im not telling you this is definitley your problem, but it is what happened to me.