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 the entire PCV system.
CAUTION:
If a PCV system component becomes clogged, all crankcase ventilation will stop and serious engine damage could occur.
Although the following manufacturers' service procedures give specific service intervals, it is recommended that the PCV system be serviced more frequently if vehicle is operated under severe conditions (extreme dust, prolonged idling, trailer hauling or short trips in cold weather).