my car at idle makes a really loud hissing noise, along with a sloppy idle it revs up to like 1600 then drops to about 500 nearly stalling and shaking.
sounds like there is a terrible leak, but i can't seem to find it.

any help?

 

there might be a vacuum leak somewhere

 

throttle body, clean it....let me find the thread about it. (not sure about the hissing noise)

 

brake kleen, its your friend.

Put the little tube on it and slowly spray around all the vacuum hoses and any gaskets...when engine changes way its running you found your leak

 

https://www.cobaltss.net/forums/2-0l-lsj-performance-tech-47/idle-problem-cure-finally-116051/

 

I've cleaned the throttle body 2 times over the course of a few weeks with no affect, and a lot of people have even replaced it without it changing the bouncing idle.