You very likely have a vacuum leak.
My preferred method for finding the general area of a vacuum leak is to use a propane bottle to spray small amounts of propane gas in the engine compartment, moving slowly and while the engine is running, and listen for the engine to spike up (even slightly) in RPM. Once the general area is known it doesn't take to much effort to find the leak itself. I use propane because it leaves 0 mess behind as opposed to solvents which can damage plastics, etc...
I would remove the air cleaner before I started, in your case, since it is likely near or around the throttle body or intake manifold.