In the controls settings screen you'll see tabs for Controller 1 and Controller 2. Assuming your pedals are part of Controller 1, you just need to adjust the sensitivity for the axis your throttle is on.
For example, in the MAPPINGS tab my throttle is set to "JOY1 Y-". I can then go to the CONTROLLER 1 tab and change the "Y AXIS SENSITIVITY" to adjust the throttle sensitivity. If you change the sensitivity while applying a small amount of throttle you will see the difference it's making (to confirm that a higher sensitivity setting is having the desired effect; sometimes depending on what you're adjusting you actually need to lower the sensitivity).
