I have had a similar problem. Not that high of idle though and not while driving. Mine does it occasionally when I am in cruise and put directly into neutral without disengaging the cruse-control first.

It then sometimes idles at around 1000-1200 RPM only while at a stop. It will continue doing this until I turn the car off and on. Like I said, this doesn’t happen every time.

In my opinion I think that this problem is not mechanical but a computer error or malfunction. Now on the other hand, the knob to manual adjust idle could have been moved, but due to the fact that your problem is not consistent, I don’t think that this could be the problem. The key to your problem is in figuring out what exactly causes the problem. If it is mechanical error then plugging the car into a computer will tell you what all is going wrong.

Try and have your car computer tested if they can, or even having it re-flashed.

I own a 2001 Pontiac Grand Am. In July 2005 my car was taken to Ed Schmidt Pontiac dealership in Perrysburg, Ohio for a lower intake gasket repair. Almost immediately after that repair, the vehicle started to experience intermittent but frequent high idling--sometimes up to 2800 rpms. I was literally constantly braking so that I could stay within the speed limit. The vehicle was taken back to Schmidt's a couple of times but they could not get the problem to duplicate, therefore no solution. The problem continued for several months with no solution. In trying to solve the problem, the idle air control valve was replaced (didn't solve the problem), the fuel injection o-rings were replaced (didn't solve the problem). It's like these guys didn't know what the heck they were doing so they were just replacing parts. Fortunately I was not charged but I can't believe that these so-called "technicians" can't figure this out. And I was charged for 2 days of car rental because they said the o-rings needed to be replaced anyway. They never even called me ahead of time to let me know they were going to do this -- and it didn't even fix the problem. Finally, on March 31, 2006, while my car was idling high on the way home from work, I decided to drive it right to the dealership where they could actually hear and witness the problem. They hooked up some kind of meter to read codes while it was idling at over 2000 rpms. They kept the car over the weekend and on the following Monday I was told I could come and get the car. The very next day the same problem occurred. And the next day (today April 5, 2006). Long story short -- the technicians at Ed Schmidt Pontiac in Perrysburg, Ohio do not know what they are doing and I tell everyone not to go there. I have decided to log what happens to the car every day and I will contact Pontiac headquarters and lodge a complaint. I think at this point I should get a new engine, free of charge!!