A combustion-powered fastener-driving tool, comprising: a tool housing; a power source associated with said housing and including a cylinder head, a cylinder and a piston reciprocating in said cylinder, a valve sleeve reciprocating relative to said cylinder, a chamber switch and a trigger switch, said cylinder head, said cylinder, said valve sleeve and said piston combining to define a combustion chamber, the closing of both said switches required for initiating an ignition of said power source for driving said piston down said cylinder; a fan disposed in said combustion chamber and a control system including a control program associated with said housing, connected to said power source, said chamber switch and said trigger switch, and configured for providing a designated ignition delay period after fuel is injected into the combustion chamber and when the chamber switch is closed, wherein said delay period being variable as a function of monitored tool parameters; wherein said fan is powered by a fan motor and wherein the combustion-powered fastener-driving tool is further including a fuel metering system connected to a fuel cell and configured for dispensing fuel to said combustion chamber, characterized in that - either said tool further including at least one temperature sensor for monitoring at least one of ambient temperature, engine temperature and fuel cell temperature, said at least one temperature sensor being connected to said control program, said control program extending said delay period with decreasing temperatures; - or said control system monitors operation of said fan motor, and said program is configured for varying said delay period as a function of speed of said fan motor; - or said control system is configured for monitoring fuel pressure emitted by said fuel metering system and varying said delay period as a function of fuel pressure. a tool housing; a power source associated with said housing and including a cylinder head, a cylinder and a piston reciprocating in said cylinder, a valve sleeve reciprocating relative to said cylinder, a chamber switch and a trigger switch, said cylinder head, said cylinder, said valve sleeve and said piston combining to define a combustion chamber, the closing of both said switches required for initiating an ignition of said power source for driving said piston down said cylinder; a fan disposed in said combustion chamber and a control system including a control program associated with said housing, connected to said power source, said chamber switch and said trigger switch, and configured for providing a designated ignition delay period after fuel is injected into the combustion chamber and when the chamber switch is closed, wherein said delay period being variable as a function of monitored tool parameters; wherein said fan is powered by a fan motor and wherein the combustion-powered fastener-driving tool is further including a fuel metering system connected to a fuel cell and configured for dispensing fuel to said combustion chamber, characterized in that - either said tool further including at least one temperature sensor for monitoring at least one of ambient temperature, engine temperature and fuel cell temperature, said at least one temperature sensor being connected to said control program, said control program extending said delay period with decreasing temperatures; - or said control system monitors operation of said fan motor, and said program is configured for varying said delay period as a function of speed of said fan motor; - or said control system is configured for monitoring fuel pressure emitted by said fuel metering system and varying said delay period as a function of fuel pressure. - either said tool further including at least one temperature sensor for monitoring at least one of ambient temperature, engine temperature and fuel cell temperature, said at least one temperature sensor being connected to said control program, said control program extending said delay period with decreasing temperatures; - or said control system monitors operation of said fan motor, and said program is configured for varying said delay period as a function of speed of said fan motor; - or said control system is configured for monitoring fuel pressure emitted by said fuel metering system and varying said delay period as a function of fuel pressure.