A little bit about NVTCS (Nissan Valve Timing Control System):

A hydraulic mechanism in the hub of each intake cam (driven by a single-row chain) changes inlet timing relative to outlet timing. At low and intermediate speeds, earlier intake valve closing improves air pumping efficiency and idle quality. At high speeds, later closing enhances torque output. To achieve this phase change, oil pressure moves the shaft backward along a helical gear, twisting it slightly. A solenoid operates the hydraulic control valve according to a signal from the computer, which takes airflow, rpm, coolant temperature, and throttle position into account before issuing commands. When the solenoid is energized, the cam is advanced to give 28 deg. of intake/exhaust overlap. De-energized, there's only 8 deg. The NVTCS is actually quite simple, and, except for the possibility of computer input problems, shouldn't cause much trouble.