A new and improved combustion-powered fastener-driving tool utilizes a new and improved single component in-take/exhaust valve member which integrally defines both the intake and exhaust valves thereon. The intake/exhaust valve member is axially movable within the combustion chamber, and operatively cooperates with wall structure of the combustion chamber. When the intake/exhaust valve member is disposed, for example, at a first upper position, both the intake and exhaust ports defined within the wall structure of the combustion chamber are closed so as to permit the ignition and combustion phases of the tool-firing cycle to proceed, whereas, conversely, when the intake/exhaust valve member is disposed, for example, at a second lower position, both the intake and exhaust ports within the combustion chamber are open so as to permit incoming air to scavenge combustion exhaust products and to subsequently mix with injected fuel in preparation for the commencement of another tool-firing cycle.