AIR-FUEL RATIO CONTROL SYSTEM FOR AN AUTOMOTIVE ENGINE

A first lookup table is provided for storing a plurality of basic fuel injection pulse widths from which one of pulse widths is derived in accordance with engine speed and intake-air pressure. A second lookup table is provided for storing a plurality of maximum correcting quantities for correcting a derived basic fuel injection pulse width in order to correct deviation of air-fuel ratio due to change of valve clearance of the engine. A necessary correcting quantity is obtained by multiplying a learning coefficient and a derived maximum correcting quantity. A desired fuel injection pulse width is obtained by adding the necessary correcting quantity to the derived basic fuel injection pulse width. The learning coefficient is updated by 1/2 at every updating.