Check the crankcase inlet air filter (or breather filter), which is usually located in the air cleaner.
- As the filter does its job, it gets dirty.
- If it is oil soaked, it is a good indication that the positive crankcase ventilation (PCV) system is not working the way it should.
- When the filter becomes so dirty that it restricts the flow of clean air to the crankcase, it can cause the same problems as a clogged PCV valve.
- So be sure to check this particular filter when checking the PCV system and replace it as necessary.
The entire PCV system should be inspected. Courtesy of Nissan Motors.