Can't Identify an Air Hose

I have a 2005 Buick Century with a 3.1L V6. There is a plastic air hose, about a half inch diameter, connected to the top of the intake air duct, between the mass airflow sensor and throttle body. The other end is connected to the back of the engine near the firewall. Can anyone tell me what it is and does? I found it disconnected at the engine end, so I just snapped it back into place. It might have gotten dislodged when I replaced my IAC valve.

That may be the PCV hose.

The PCV system removes crankcase gases from the engine to be reburned in the engine.



That is the breather hose for the PCV system.