i have a 2001 m5 w/4500 miles, babied to the extent that an M5 can be babyed to. but when i went to turn on the car it would stay on. it wants to turn over and a few times it did, it would rev to it's idle and then drop and shut off. i always fill up 93 amaco went to mobile once a week & 1/2 ago then went back to amaco but not my usual station. and i'm already 1/2 tank into the gas. the engine also started knocking a few times when it turned over once. i think it might be water in the gas, but would the car react i that way? anyone with some sort of an idea as to what might have happened. THANK YOU EM PWR(PAUL)