fuel ratio feedback correction coefficient lambda is decreased at a certain gradient incidentally the relation of pl gt il is established fig7 shows the learning routine which is conducted as the background job to set and renew the learning correction coefficient klrn accordingly this routine corresponds to the learning correction coefficient renewing means at step 31 it is judged whether or not u03bb control flag is 1 if u03bb control flag is 1 the routine ends the reason is that learning cannot be performed when the feedback control of the air fuel ratio is stopped at step 32 it is judged whether or not predetermined learning conditions are established when the water temperature tw is higher than the predetermined value the area of the engine driving state is set by the engine revolution number n and basic fuel injection quantity tp the frequency of the reversion of lean and rich signals is larger than a predetermined value for example 3 and the engine is in the stationary state it is judged that the learning conditions are established if these conditions are not satisfied this routine ends in the case where the predetermined learning conditions are established while the feedback control of the air fuel ratio is conducted and the area of the engine driving state to be learned is set the routine goes into step 33 and the mean value of u03b4a and u03b4b is determined stored u03b4a and u03b4b are upper and lower peak values of the deviation from the reference value of the air fuel ratio feedback correction coefficient lambda that is 1 between the reversions of the air fuel ratio feedback correction coefficient lambda in the increasing and decreasing directions as shown in.