Abstract: An air inlet auxiliary device provides additional air to an inlet manifold of a vehicle. The auxiliary device includes a main body, a filter assembly mounted to a first end of the main body, a control seat mounted to a second end of the main body and in fluid communication with the inlet manifold, and first and second cylindrical members mounted in the main body. Air passages are defined in the first and second cylindrical members. When the engine of the vehicle is idling or runs under a speed slower than a pre-determined value, more additional air is supplied to the air manifold, and when the engine is running under a speed faster than the pre-determined value, only a small additional amount of air is supplied to the inlet manifold.