Is it the flybridge control or both? Here is some information I have found on these controllers:
"As far as a system going into gear and throttling up on their own this would require a 2.5 to a 5 millamp signal being sent to the processor. I would look for a worn control head and if doubt I would replace it approx. $500 for a twin engine control head. I would also check all wire connections to insure there are no loose connections. Make sure the system was installed at least 4ft from the generator as we have seen RF interferance from some generators (the same for single side band radio wires). " Hope this helps..
Marine Mechanic
Certified Technician Mercruiser Mariner Mercury Johnson Evinrude & business owner