1980 240D Won't Shut Off

My 1980 240 D has 153k miles on it. Sometimes when I turn off the car the engine continues to run until I open the hood and push the stop lever. Why wont the engine shut off everytime? What can i do about it? Also, the cruise control on this car is messed up as well, in that when the cruse control lever is either pushed to the accellerate, decel, or engage positions, and held there, the car will accelerate. nothing happens when disengage is held down. the cruise control does not maintain the speed, and it does nothing but accellerate when those positions are pushed.