I was driving down the road yesterday and all of the sudden the car started making an odd exhaust sound, like it was idling really rough. I was driving at about 45 mph at around 3,000 RPM in 3rd I believe. It was in the 70s and I had the A/C on and I'd been driving for a hour or so. The sound and rough feeling went away only a couple minutes after it started. I'm not sure what this was but it hasn't done it since. The only things I can think of is maybe some bad gasoline? It was sitting in the shop for a few weeks so maybe some sediment went thru the lines. Anyone have any other ideas?