Q: So I just bought a 2009 Audi A4 Quattro, and all we did was change the oil, and the car started shaking. What could be the problem

Rough operation and loss of power on acceleration can be due to plugged fuel injectors, faulty oxygen sensors, fuel pump and/or filter, vacuum leaks, ignition system malfunctions, bad valve timing if the timing belt or chain is worn or skipped, blocked exhaust (e.g., catalytic converter fails or become clogged), a faulty airflow sensor or throttle position sensor, and so forth. To pinpoint the exact case will require an engine loss of power diagnostic. If you request that diagnostic, the 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.