A system and method are disclosed for regulating engine idle speed by coordinating control of two actuators: a slow actuator and a fast actuator. The slow actuator is preferably a throttle valve and the fast actuator is preferably an ignition system affecting spark timing. The slow actuator is controlled based on an idle power requirement and the target idle speed; whereas the fast actuator is controlled based on the idle power requirement and the actual idle speed. Additionally, control of the two actuators is further based on a desired power reserve and an actual power reserve. Power reserve is related to the ratio of the power produced by the engine and the power that would be produced by the engine if the faster actuator were at its optimal setting.