Es300 & RX300
ACIS is a variable induction system that improves low speed engine performance by increasing length of intake runners in air intake chamber. In accordance with engine speed and throttle opening angle, ACIS controls intake manifold length in 3 stages by opening and closing 2 Intake Air Control Valves (IACVs) that are located on end of air intake chamber and downstream of throttle valves. See Fig 1.
With engine under a heavy load and vehicle speed low, Engine Control Module (ECM) turns on both ACIS Vacuum Switching Valves (VSVs) resulting in vacuum being supplied to both IACV actuators. This results in both IACVs closing, enabling intake air chamber, throttle bodies, and air cleaner hose to function as an intake manifold. With engine under a heavy load and vehicle speed in mid-range, ECM turns on ACIS VSV on intake air chamber side and turns off ACIS VSV downstream of throttle valves. As a result, IACV in air intake chamber closes and IACV downstream of throttle valves opens, enabling intake air chamber to function as an intake manifold. With engine under a light load and vehicle speed high, ECM turns off both ACIS VSVs. This allows both IACVs to open, enabling intake air chamber to function as a normal intake air chamber.