Q: P0300 multiple misfiring and it starts but when u put in gear it really misfires?

Among the causes of misfiring are faulty spark plugs, low compression, damage or excessive wear of spark plug wires and/or coils, faulty fuel injectors, clogged EGR valves or tubes, burned valves, improper ignition timing, vacuum leaks, leaking head gasket, faulty camshaft sensor, faulty crankshaft sensor, faulty mass air flow sensor, faulty oxygen sensor, faulty throttle position sensor, faulty catalytic converter, and others. If you want the cause pinpointed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a misfiring diagnostic and the responding certified mechanic will get this diagnosed and resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.