Here in Cincinnati, it has been really cold the past few weeks. On a couple of occasions, the temperatures overnight dropped down to single digits. (one was this morning) Anyways, on these mornings with single digit lows, My car decides to hiss at me. If I rev the engine, then let off the gas a hiss is heard under the (passenger side?) of the dash as the engine falls back down to idling. Once the ambient temperature warms up or the cabin temperature warms, the hiss goes away (engine temperature may be related, I haven't really noticed) Anyways, since it only has this hiss when REALLY cold, I am not that worried but do wonder what it is. Is there a vacuum bleed off or something? Oh yeah, and when you shut the car off when it is doing this, you have hear the hiss as the engine dies and the hiss just sounds like escaping air. Anyone have any clues into the small novel I have just written (sorry)? Thanks