Apparatus for controlling engine operable on gasoline/alcohol fuel blend

An apparatus for use with an internal combustion engine operable on either of gasoline fuel and gasoline/alcohol fuel blend, comprising:

• an alcohol concentration sensor sensitive to an alcohol concentration of the fuel to be delivered to the engine for producing an alcohol concentration signal indicative of a sensed alcohol concentration;
• an oxygen sensor sensitive to an oxygen content of exhaust gases discharged from the engine for producing an air/fuel ratio feedback signal;
• and
• a control unit coupled to the alcohol concentration sensor and the oxygen sensor for controlling the amount of fuel metered to the engine, the control unit including means for calculating a basic value for the amount of fuel metered to the engine based on engine operating conditions, means responsive to the air/fuel ratio feedback signal for calculating a first correction factor based on a deviation of the air/fuel ratio from a stoichiometric value, the first correction factor being within a control range defined by predetermind upper and lower limits, means for correcting the calculated basic value for the sensed alcohol concentration, means for correcting the calculated basic value based on the calculated first correction factor to provide a closed loop air/fuel ratio control, means for clamping the first correction factor to one of the upper and lower limits to place the closed loop air/fuel ratio control into a clamped state when the engine is idling, and means sensitive to an alcohol concentration signal change exceeding a predetermined degree for releasing the closed loop air/fuel ratio control from the clamped state.