I am helping a friend with his small f/e boat.

The problem is that sometimes when you turn the joystick to control the rudder the throttle starts for no particular reason. Apart from being dangerous it also makes the boat impossible to control. It does other erratic things to like when you move to increase throttle sometime is responds sometimes it only gives haf throttle. I have removed ESC and reconnected everything properly and tried with several different batteries in the boat and transmitter. The ESC is quite new and was working fine. It is a Turnigy 35 Marine, the motor is a small brushless and the battery is a 3S 2700MAH 25C.

Any suggestions?