An electronic engine speed control system for a grass mowing machine powered by an internal combustion engine includes a microcontroller providing an output signal to an engine speed actuator for the engine, a pedal position sensor connected to a foot pedal and providing a voltage input signal to the microcontroller based on the position of the foot pedal, a PTO clutch switch providing a signal input to the microcontroller indicating if a PTO clutch is engaged, and a lever position sensor connected to a hand lever and having a range of positions including an Automatic mode position and a plurality of Manual mode positions. The hand lever position sensor provides a voltage input signal to the microcontroller in the Automatic mode position such that the microcontroller output to the engine speed actuator is related to the voltage inputs from the pedal position sensor and PTO clutch switch, and provides a voltage input signal to the microcontroller in a range of Manual mode positions such that the microcontroller output to the engine speed actuator is related to the voltage input from the lever position sensor.