Forgett all the diagnosise of the position of the wires to the throttle servo, you are using a system that does not accept RF interference, it can only be direct electrical spikes through the wiring or a bad servo. My guess is a servo gone down, the amount of vibration comming throgh the operating rod too the servo and the heat etc, is going to cause a throttle and or choke servo to go occasionally. I tend to use an Analoge coreless for both and change them at the end of each season.

Mike