1985 Mercedes CDT when put in drive will not start out in low gear. It will not downshift when accelerator is pressed to floor. Reverse works fine. Car will drive in high gear. Transmission can manually be shifted thru lower gears. What might be the most likely problem.

 

To be honest, I don't know. Normally failure to get moving would be a bad B2 piston, but if the transmission will go when you put it through the lower gears manually, I am stumped. Maybe I am just not properly understanding you.