An
engine control unit (
ECU) is a type of
electronic control unit that controls a series of
actuators on an
internal combustion engine to ensure optimal engine performance. It does this by reading values from a multitude of
sensors within the engine bay, interpreting the data using multidimensional performance maps (called
lookup tables), and adjusting the engine actuators accordingly. Before ECUs, air-fuel mixture, ignition timing, and idle speed were mechanically set and dynamically controlled by
mechanical and
pneumatic means.