Engine synchronization apparatus and system for multi-engine vehicles such as boats and aircraft providing limited authority throttle cable trim effected by an apparatus interposed between the throttle plate and throttle cable of a slave engine and mounted in a floating configuration. An actuator is mounted to the apparatus to trim the distance between the throttle plate and throttle cable attachment thereby trimming the throttle cable. A system is provided in which a difference signal derived from master and slave engine tachometer signals is used to control the actuator and synchronize the engines within a predetermined range.