If I understand your question, you are saying that the car lacks throttle response for the initial 1/3 of the pedal's travel?
If you are used to driving American or Japanese cars, you will find an MBZ gas pedal to be quite different, especially on a 300sd. What I mean by this is that older MBZ's have a long pedal travel and have a much more progressive response than does an Accord or Tuarus, for example, which will jerk your head back if driven by a beginning driver.
The only thing I can think of would be to adjust your throttle linkage possible. I am not sure of the procedure, but I am sure other members will chime in shortly.