Identify this part!

[sleepingboxster]

Thanks. I just capped off the vent to see what would happen. Nothing seemed to change . The hiss was still there, maybe it's normal for the AOS to hiss. Before when I capped off the breather hose to the AOS The check engine light immediately went away. when I capped the vent it did not. Is the PCV a common failure spot, is the leaking from the pcv when it's not connected to the aos normal.