The IC engine has emission sensors (26, 27) on both sides of the catalyst (13) in the exhaust system. A CPU (31) computes the fuel/air mixture on the input side of the engine and monitors the exhaust quality both sides of the catalyst. A self adjusting control measures the effects the discrete changes in the fuel air/mixture on the exhaust quality and adjusts the engine management for optimum operation to reduce emission products and to prolong the life of the catalyst. The system is a sell learning system which automatically sets the upper and lower limits of the fuel/air mixture and its effects on the exhaust quality. The CPU identifies the change over between rich and lean mixture for a precise setting of the fuel input.
