HVAC leak?.....

I think i have an air leak in the HVAC. Its an air leak sound or hissing sound in the dash. Not sure where at in the dash but the sound goes away when i run the AC or heat. But as soon as i turn it off the sound comes back. If i gas it then the sound will die down but will come back if i let off the throttle. Any ideas? what should i be looking for?

You have a vacuum leak probably in the control valve for the HVAC. That is the hissing sound you are hearing. The book I have does not give the location of the vacuum control valve but it is under the dash somewhere. Someone else may know where to find it and can help you out.