An engine idle speed control system and a method for a vehicular gear are provided. The system includes an electronic controller, an engine connected to an ignition unit and a fuel supply unit, a battery, a starter switch connected to the battery, and a starter motor connected to the starter switch. The engine has a gear mechanism and a clutch which is connected to a clutch lever. The electronic controller is connected to a vehicle speed sensor, a throttle position sensor, and an engine revolution speed sensor. The clutch lever with a node switch provides a lever node control signal, the gear mechanism with a gear node switch provides a gear node control signal, and the electronic controller is connected to the node switch of the clutch lever and the gear node switch of the gear mechanism, so as to control automatic idle speed stop and start of the engine.