Reset the FBW throttle module (whatever it's called).
If you search for throttle hesitation in general 300 discussions, you'll find it there. There was some contoversy as to weather it actually does anything and what's exactly the right way to do it, but I noticed an improvement resetting it.
As I recall the procedure (which worked)....
Turn the car on to the run position but do not start
Slowly and evenly press the throttle to the floor and back up. Generally, about 6-8 seconds down and the same back up. You do not need to hold it to the floor, just all the way down and back up smoothly.
Turn the key to the off position and wait about 15 seconds.
Go for a ride and test it out! If it didn't reset, repeat all above. The key parts as far as I can tell is to press the pedal down and up slowly and evenly and to wait a bit after turning the key off at the end.
Good luck!