I think you are looking at the throttle cable. That would not be what you want to adjust. In this picture you CAN see a cable adjustment though. The black nut at the end of the cable housing; where it attaches to the metal bracket (midway up the washer reservoir).
If I am right about this being the throttle cable, look around, the trans cable is a similar arrangement. Remember, one cable pulls and one is PULLED.
Bosch Master, ASE Master, L1
33 years MB technician