Neither - look at the linkage under the car, trace it back to the streeging servo - the motor that makes the linkage move. Unscrew the screw that holds the arm the linkage is attached to from the servo. Look under the arm, there is an insert where it attaches to the servo (may stay on the servo) - check that (you may need a magnifying glass to really see its condition) the teeth are in good shape.

The way strg is jumping, sounds like some of the teeth in the insert have stripped, letting the servo spline skip inside the insert.