Q: my car jerks and wont accelerate past 20 mph

The loss of power and the brake issue have separate causes. Vibration on braking is usually due to defects in the brake rotors, particularly warping and thickness variation in the rotor. Improperly mounted rotors can also cause vibration. To resolve the brake issue, just request a brake system inspection. Among common possibilities for the loss of power are throttle body faults (electronic throttle controls, mass airflow sensor, torn air intake hose), worn out spark plugs, faulty fuel pump or restricted fuel system, and large vacuum leaks (including EGR malfunctions, PCV system, leaking intake manifold, leaking EVAP purge valve). A scan tool would be used to look at real time conditions within the engine (particularly fuel trim, etc.) and identify the root cause. If you want the required diagnostic tests performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a loss of power inspection/diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.