I have had a sporadic vacuum leak for the past several months. Some days the engine shuts off right when I turn the key off; some days it takes a few seconds for the engine and some days it takes up to 5 seconds. I have noticed that when the engine does not shut off right away, there is a fizzling sound coming from the key ignition area. It seems pretty obvious that there must be a vacuum leak somewhere close the key. Also the transmission shifts perfectly when the leak disappears and not nearly as well when the leak is present.