Avalon, Highlander 3.0L V6 & Sienna
Acoustic Control Induction System (ACIS) is a variable induction system that improves engine performance by increasing the length of intake runners in the air intake chamber. In accordance with engine speed and throttle opening angle, ACIS controls the length of intake runners in air intake chamber in 3 stages by opening and closing the 2 intake air control valves located on end of air intake chamber and downstream of the throttle valves. See Fig 1.
When engine is under a heavy load and vehicle speed is low, Engine Control Module (ECM) turns on both ACIS Vacuum Switching Valves (VSVs) resulting in vacuum being supplied from vacuum tank to both actuators for the intake air control valves. ACIS VSVs may also be referred to as intake air control valve VSVs. This results in both intake air control valves closing, enabling the air intake chamber, throttle bodies and air cleaner hose to function as an intake manifold. When engine is under a medium load and vehicle speed in the mid-range, ECM turns on ACIS VSV at the air intake chamber side and turns off ACIS VSV downstream of the throttle valves. As a result, the intake air control valve in the air intake chamber closes and intake air control valve downstream of the throttle valves opens, enabling air intake chamber to function as the intake manifold. When engine is idling, engine is under a light load or vehicle speed is high, ECM turns off both ACIS VSVs. This allows both intake air control valves to open, enabling air intake chamber to function as a normal air intake chamber. ECM uses an engine RPM input signal and throttle position sensor input signal for determining ACIS operation. Engine RPM input signal is provided by camshaft and crankshaft position sensors.