1999 Mercury Mystique • 4 cylinder 2WD Automatic •

I have a 1999 Mercury Mystique 4cyl. I came off the interstate and noticed that while braking, the car still had a lot of power. It would not down shift. I put it into neutral, just to come to a stop. I shut off the engine and restarted. The tachometer shot straight up to 4000 and the car shook hard. This repeated each time I restarted the car. I disconnected the battery for 1 minute, reattached it, and when I started the car, it started and idled normally. Staying in park, I pushed the accelerator down, revving the engine, it will approach and stay at 4000 RPM. There was no engine light displayed during incident. What might cause this problem?
December 30, 2010.

Check to make sure there is no damage to the throttle cable. If the check engine light is on, have the computer scanned. Also, check to make sure idle air control valve is working properly.