I'm trying to find out how to check for vacuum leaks. This is what happens, I start my truck in the morning and it does fine. I drive somewhere turn it off and go in for a couple minutes come back start the truck again and sit there for a little bit just idleing. After a few minutes it starts to idle rough and if I let it sit there like that for a while it almost stalls. When this starts white smoke starts coming out the exhaust pipe and is put put putting lol. Someone had mentioned to me before it could be the throttle body or the IAC valve but the high pitched hissing sounds like an air leak to me. also while driving down the road if I let off the gas a little bit you can hear the high pitched hiss come from the engine for a couple seconds. I'll post the same video up here it is.

http://www.youtube.com/watch?v=tYZ6mzOyqtg

 

Sounds like the IAC on back of the TB. Remove it, and clean it and the bore to which it goes into on the TB.