I assume you performed a Throttle Position Reset? Mine did (or didn't) do the same thing on initial install.

1. Turn the ignition key to the on (not start) position.

2. Press the gas pedal to the floor and hold for five seconds.

3. Turn the key to the "off" position (don't remove the key), then release the gas pedal.

4. Wait at least two minutes for ECU to reset.
Or
1. Get in your car, it doesn't matter if you close the door or not.

2. Turn the key to the on (not start) position.

3. Press the gas pedal to the floor with the key in the "on" position.

4. Hold the pedal to the floor for five seconds, then turn the key back
to the "off" position (don't remove the key), then release the gas
pedal.

5. Wait 2 mins. for a full alignment.

6. Drive the car as you always do.


Key on, pedal down, 5 sec, key off pedal up, wait 2
minutes. Keep the key in for the entire thing.

And this is from BenzWorld:

Reset Throttle Body
Open the door, put the key on the ignition, close the door.
Move start switch into position "2"
Press the gas pedal to the floor... past the kick down point
Hold the pedal there for 15 seconds
After 15 seconds while foot still planted, turn the key off but do not remove it
Release gas pedal... Wait at least 2 minutes while not touching anything in the car, don't open the door even.
After the 2 minutes start the car and drive off normally...