Apparently the throttle body for "fly by wire" cars can become lazy and not open fully. On some other cars it is possible to reset it using the following method.
Insert key and turn to 1 so the electrics are on but the engine is off.
Press the accelerator pedal all the way to the floor (including kickdown if you have it).
Hold the pedal down for 5 seconds and turn the key back to 0.
Now release the pedal.
Wait a minute or so before starting your car.
edited; i found this on a UK smart roadster forum.
Insert key and turn to 1 so the electrics are on but the engine is off.
Press the accelerator pedal all the way to the floor (including kickdown if you have it).
Hold the pedal down for 5 seconds and turn the key back to 0.
Now release the pedal.
Wait a minute or so before starting your car.
edited; i found this on a UK smart roadster forum.