you possibly have a faulty petentiometer on the throttle pedal,remove plug from pedal and check for water ingress..or a wiring fault,which would generally fail where the cab tilts and flexes the loom ,identify loom you require and check for chaffing...wire numbers are 4677, 4678 ,4679, 4166 ,4680 ..check them for shorting to earth and for open circuits with a mutimeter
norb, January 2013