Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
There may be a problem with the idle air control circuit but you will want to make sure that the throttle body and idle air passages are clean.
You may want to do a throttle body cleaning on it. You can follow the directions on the can but you will want to make sure that you give it a few shots with the throttle plate closed, so that the cleaner can get into the idle air passages.
Of course, you will want to make sure there are no vacuum leaks and that there is not any un-metered air that is entering into the intake, thanks