Its still for Positive Crankcase Ventilation. The valve is on one side, but the air for ventilation needs a place to go in, and a place to come out. I think the "dirty" air comes out of the drivers side and into the intake tube to be burnt in the combustion chambers. I'd have to go out and look at my engine to be sure, and its really cold out there so you'll have to wait for confirmation from someone else.
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