Have you removed the throttle body. The O ring is a known problem not lining up an staying in place, when reinstalling. Or it may have just ruptured. You say you can hear it sucking air ..that is a problem.. we all use different methods when checking for vacuum leaks. I use either WD40 or carb cleaner. Spray ,w/ engine running, where you feel the air is leaking or a open vacuum is. The idle will either up or down depending or its routing...sounds like this is driving you crazy...lol