I have a problem with the throttle (gas pedal) control. It works normally, but if you press and release (for example when accelerating), engine continues to rev up for a while, about 1 second. For example, when I release the gas pedal at 3000, it goes higher till 3500 and then goes down; or it stays at 3000 for a while and then goes down.
What is wrong with the engine?

Thanks.