WARNING: This page is about a different car, the 2013 Acura MDX, 2012 Acura MDX, 2011 Acura MDX, and 2010 Acura MDX. However, it is still accessible from the selected car via links, so may be relevant.
The PCV valve prevents blow-by gases from escaping into the atmosphere by venting them into the intake manifold.
Fig 1: Positive Crankcase Ventilation (PCV) System Operation Diagram