The OEM PCV valves on the 1990-1996 Nissan 300zx TT should be replaced every 60,000 miles. Over the years, the Nissan PCV valves start to get clogged and hurt the performance of the Nissan Z. Original PCV hoses get brittle, and break during installation. It's recommend that they get replaced. This set includes 2 PCV valves and 5 PCV Hoses.