Check the switch. I do not know if your cruise switch is like mine, but if it is, then it will set when moved up or down. Try to set it by moving it down and see what happens. Your switch might be getting stuck and thus remains in 'accel' when you set it 'up'. If you set it 'down' it shouldn't happen if this is the case. If your switch is different and none of this applies, contact Peter at GDL and find out how to test the switch. If you get lucky it will be the problem.
1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick