All of a sudden, my 79ZX has decided to idle at about 1200rpm. When I turn the a/c on, idle drops back to normal (800-900rpm). It's almost as if the aux air regulator were stuck open, but it's not. Anything else that would bypass too much air into the engine and cause a high idle? I don't know if it's related, but my BCDD is making a nasty hissing/squealing sound (kinda' like pinching a balloon's filler hole while you let air out of it) when I let off the gas.

And why the heck would it behave correctly with the a/c on?