Hi Karen, sounds like either your throttle cable is sticking or the idle speed control actuator is sticking, get someone to have a look at the movement of the throttle flap under the bonnet while you press the accelerator pedal to make sure the flap is returning to the idle stop, if thats ok then you will have to remove and clean the idle valve actuator as these often get gummed up with petrol deposits that need to removed with "carb cleaner" spray don't use anything else like WD40
nigel, May 2008