Abstract: An electronic ignition timing system which cooperates with an adaptive closed loop fuel control system to provide more rapid heating of an exhaust catalyst by retarding the ignition tinning during colds starts only after an index of maturity value has been generated to indicate that fuel control parameters which characterize an individual engine have been adaptively learned and are available to operate the engine with a lean mixture during cold idling conditions. The index of maturity value alters the mode of operation of the fuel control mechanism to provide robust rich operation prior to adaptation and a more aggressive lean mode operation after the adaptive parameters have been developed which permit optimized operation, and alters the ignition timing to retard the spark to more rapidly heat the exhaust catalyst.