Engine fuel control device and idling air-fuel ratio control method

An engine fuel control device, comprising:

• a fuel supply means that supplies an engine with a fuel;
• a mixture ratio determination means that determines a mixing ratio of the fuel and air;
• a mixture introduction means that introduces the air-fuel mixture, whose mixing ratio has been established, into the engine;
• a first throttle valve that is disposed in an intake pipe of the engine;
• a bypass passage that bypasses the first throttle valve;
• a second throttle valve that is disposed in the bypass passage;
• a target speed setting means that sets a target engine speed during idling;
• a throttle valve opening control means that controls the opening of the second throttle valve so as to maintain the target engine speed;
• a control factor setting means that sets a factor so as to control the opening of the second throttle valve;
• a capturing means that captures a change in a state of the factor;
• and
• a control means that controls the mixture ratio determination means based on the change in the state of the factor captured by the capturing means.