There are other mechanical factors which could contribute to this condition. Despite means of actuation, be it mechanical or electronic, there's still a valve which controls volume of air, which controls engine speed. Though unlikely, it is possible it may become stuck, say, if the throttle body is caked in deposits from recirculatory emissions systems. Furthermore, a leak down stream of the throttle plate will also allow uncontrolled air flow into the engine, which will increase engine speed uncontrollably. Also unlikely, but still possible.
Sent from my LG-H910 using Tapatalk
Assumes engine CPU doesn't notice the engine speed doesn't jive with throttle position and cut fuel.