My wife and I were driving our 2011 Audi A3 from L.A. to Flagstaff AZ. We got diesel in Barstow CA then drove about 300 miles when the glow plug then check engine light came on. The car wouldn't exceed 60 mph. Once towed to a repair facility, the service manager insisted that we accidentally put unleaded gas instead of diesel. I know I filled the tank with diesel. Here's my question: assuming this car had 13 gallons of unleaded gas as this service manager insists, is there any way it could have gone 300 miles before showing a problem?