Positive Crankcase Ventilation: Maintenance: Notes
Although the following manufacturers' service procedures give specific intervals, it is recommended the crankcase ventilation system be checked more frequently if vehicles are operated under severe conditions (extreme dust, prolonged idling, trailer hauling or short trips in cold weather).
NOTE:
An engine may idle slow or rough due to clogged PCV system. Never adjust carburetor without first checking PCV system. See TESTING in this article. If the PCV system becomes clogged, all crankcase ventilation will stop and serious engine damage could result.