An idle down controller for pressure washers is responsive to the drop in pressure at the pump outlet. The controller includes a sensor disposed in the pump outlet manifold. When the fluid is being bypassed, the manifold pressure drop is communicated to an actuator. The actuator overrides the engine governor and forces the engine throttle to the idle speed. When an operator is discharging a pressurized fluid, the actuator allows the governor to operate the engine at its normal speed.