I have a manual-transmission 2008 Ford Fusion SE. It's a great car but I have been having some problems with it recently. Firstly, the throttle does not seem to close when I let off the gas pedal. If I take my foot off the gas pedal without taking the car out of gear, The engine RPM does not decrease at all and the car will carry along at its current speed. Putting the car in neutral makes the RPM increase until I come to a complete stop, where the engine finally begins to run at its idling RPM. How should I go about diagnosing this problem? I just got it out of the shop, so the mechanic obviously overlooked it.