You might try to re-center the throttle servo - take the servo horn off and then turn the car on. Let the servo re-center then without moving the servo drive spline, put the arm back on, then turn car off. When you turn radio on set trim back to zero and turn car on. See if it is any better.
If servo had gotten off center, this should make a diff. If servo was not off center, you'll have to add the trim again to get back where you were.