The PCV (positive crankcase ventilation) system draws filtered air from the air cleaner and routes it into the engine. (This PCV inlet hose also is the terminus for the small nylon pressure reference line for the fuel pressure regulator.)

The air circulates throughout the crankcase and blends with blowby gas and is then drawn out of the engine on the small PCV hose that routes to the inlet manifold. This way blowby gases are consumed in combustion. All cars sold in the US have required such systems since 1963 (1961 in CA).

A normal engine inspection (such as during a 15K of 30K mile service) should include inspecting all hoses - coolant, vacuum, PCV, and fuel.

Duke