Idle speed fluctuates, then turns off?

While in park, my car starts to rev fluctuating between 1000-2000 rpm, and shuts off in about 8 seconds of doing this. It also revs sometimes while in drive on its own very slightly. I recently took the air intake hose out to try and take out the intake manifold and messed with some stuff, had the intake hose bent for a minute, put it back with a new clamp, cleaned the air intake manifold, stopped revving then started doing it again after driving for a minute. It was also making a hiss noise the first time I put it all back, now I kind of hear the same noise. Also, my gas is draining fast, tonight I put it in park and it shut down with a loud engine noise as well.