Abstract: A brake booster system for a motor vehicle of a type having an internal combustion engine without a conventional throttle-type valve in an intake manifold for engine output control. In accordance with the present invention, a throttleless-type IC engine of the above described type is modified to include a valve which can periodically close or obstruct the path of intake air to the IC engine to generate intake manifold vacuum to provide a needed pressure differential for brake booster operation. The system includes a pressure transducer which controls operation of the valve to provide the desired control of engine brake booster vacuum.