The whole car shakes when I hit the speed 42mph -45mph. It only does it when the car is warm, after 20 mins of driving, but not when the car is cold. I've recently had new tires, rotors, head gasket and timing belt done. The same week I had the timing belt done, the engine light came on and the scanner says "warm catalyst below threshold." Would this cause the car to shake? What are symptoms of a bad converter? The engine has good pick up & there is no loss of power.