As with the rack and pinion type steering, preload is very important. If the preload is not correct, it could result in such trouble as steering wheel play or shimmy or lack of durability, so always make sure that it is correct. SST SR160N PPS (Progressive Power Steering) In addition to the power steering functions, the PPS controls hydraulic pressure acting on the hydraulic reaction chamber located in the control valve of the gear box to change steering characteristics according to the vehicle speed. As a result, the wheels can be turned more lightly at low speeds or when steering during the vehicle stopped, while a responsive steering feeling is assured at medium to high speeds. Power Steering ECU Vehicle Speed Sensor Vane Pump Steering Gear Housing SR2894 Torsion Bar Rotary Valve Hydraulic Reaction Chamber SR2895 IDLE-UP DEVICE The pump produces the maximum fluid pressure when the steering wheel is turned fully to the right or left and causes a consequent increase in load on the pump which causes a decrease in engine idle rpm. To solve this problem, vehicles are equipped with an idle-up device which acts to raise the engine idle rpm when there is a heavy load on the pump. On EFI engines, when the piston of the air control valve is pushed by fluid pressure, the air valve opens and the volume of air passing the throttle valve is increased to regulate engine rpm. Air Flow Meter Surge Tank Steering Gear Housing Air Control Valve SR2892 The idle-up device functions to raise engine idle rpm when pump fluid pressure acts on the air control valve, installed to the pump body, to control the flow of air.