Hello, all. I have a '89 Merc Marquis that has an annoying hiss sound coming from the engine area upon startup. It is in relation to the throttle ( when you give it gas, it slows but is louder again at idle). Also, when I put in gear (reverse, drive, neutral) it slows off but then comes on again. While driving it is noticeable, to me at least, and is driving me crazy. I have checked the vacuum canister (looks like a large tin can on drivers side of engine bay) and the hoses seem to be tight. Anyone have a suggestion or similar situation? I have just gotten the car, and it is my first FORD product. Thanks in advance!