An engine speed control system for an agricultural vehicle includes a variable throttle controller, a mode selector, and a control device. The variable throttle control permits an operator to select a variably adjustable engine speed and the mode selector permits the operator to select between a plurality of pre-set engine speeds. The control device receives output signals from the throttle controller, generates engine speed commands, and delivers the commands to an engine controller for controlling the speed of the agricultural vehicle's engine. The control device is operable to generate a first engine speed command associated with one of the pre-set engine speeds when an operator activates the mode selector and to temporarily or permanently override the first engine speed command with a second engine speed command associated with the throttle controller when the operator activates the throttle controller.