Hi guys the fuel gague in my 1984 300sd is bobbing up and down when i drive, when stopped with the key on and engine off it will stay put at where i would guess my fuel reading is.
any toughts on this??

My guess would be that your fuel sender fell apart in your tank. Assuming the sender works like a w123 that is
Dampening/anti slosh is accomplished by only allowing a very small amount of fuel to move in/out of the sender tube. If the bottom nut loosened, the sender float would be free to move as fuel sloshes in the tank.