Intake Manifold Tuning System
When engine is operating in low-to-medium speed range (approximately 4,000 RPM maximum), Powertrain Control Module (PCM) turns ON power transistor in order to turn ON intake manifold tuning solenoid. See Fig 1. Consequently, intake manifold vacuum that is stored in vacuum tank acts on vacuum control actuator, thus causing control valve at secondary port of each cylinder to fully close. Even if intake manifold vacuum decreases during a high-load operation, vacuum from vacuum tank maintains control valve fully closed.
When engine is operating in high-speed range (approximately 4,000 RPM minimum), PCM turns OFF power transistor in order to turn OFF intake manifold tuning solenoid. Consequently, intake manifold tuning solenoid introduces atmospheric pressure to vacuum control actuator, thus causing control valves of secondary ports to fully open.