Service Procedures: Notes
An engine may idle slow or rough due to a clogged PCV valve or system. Never adjust idle speeds without first checking entire PCV system.
CAUTION:
If a PCV system component becomes clogged, all crankcase ventilation will stop and serious engine damage could occur.
Although following manufacturers service procedures is recommended, PCV system should be serviced more frequently if vehicle is operated under severe conditions (extreme dust, prolonged idling, trailer hauling or short trips in cold weather).