A method and system for controlling a temperature of an exhaust gas being introduced to a catalyst is provided. Using an adjustable flow controller, an adjustable amount of tempering fluid is provided to the exhaust gas prior to the exhaust gas proceeding to the catalyst. A sensor senses a parameter indicative of a temperature of the exhaust gas being introduced to the catalyst. A computer processor uses a relationship to relate the parameter to an adjustment of the adjustable flow controller that will adjust the amount of tempering fluid provided to the exhaust gas and change the temperature of the exhaust gas being introduced to the catalyst toward a target temperature. Adjustment of the adjustable flow controller is initiated by the computer processor to change the flow of the tempering fluid, and the relationship between the parameter and the adjustment of the adjustable flow controller is updated.