For almost a year after purchase, I experienced problems with gas pedal vibration on my Volvo C70. I took it back to the dealer many times with this complaint. They would go with me for test drives but their answer was always that there was nothing abnormal about the gas pedal vibration. Hello! A gas pedal shouldn't vibrate! That in itself is abnormal! Anyway, after taking the car in for one of its regularly scheduled maintenance sessions, they changed the spark plugs and I haven't had the problem since.