Coupled with what Jager said, was just thinking about it and it sounds vaguely similar to behavior I used to get. Is yaw set to one of the toe brakes? When you start the engine, does your plane just want to go in a circle, and if you push the toe brakes it goes the other way? It's assigned to one of the toe brake axises, and you just need to assign it to the actual pedal axis as Jager described.
Wiley.