An exhaust control system for an internal combustion engine having a plurality of actuators wherein each actuator controls a predetermined engine parameter. A plurality of sensors are also associated with the engine and each sensor provides an output representative of an engine operating condition. The control system includes a PID controller associated with each actuator and in which each PID controller has an input, an output and a feedback between the input and the output. A distribution function circuit is operatively connected in series with the inputs of the PID controller. The distribution function circuit receives an error signal representative of the difference between a target value and an actual value of one or more engine operating conditions, previously determined control factor values and the feedback from each PID controller as input signals. The distribution function circuit varies the input to each PID controller as a function of the distribution function input signals.