Car has been running great but hasnt been driven much in the past few weeks. My girlfriend drove it this morning 50 miles then when she got off the interstate the car was running rough at idle. No engine lights on at all. She says she can rev it up fine and going down the roads at normal speeds is fine but when she stops and takes off it has a shudder/studder/shake to it. I am no where near the car right now so not sure what it could be ? She just filled up, and I was thinking she might have gotten some bad gas ?