teh car was driving fine til we got some gas the other night then all the sudden it spits and sputters changed the coil pack and plugs and wires cleaned the oxygen sensor put on computer and shows no problems mechanic says its got a cylinder gone down ok so how does a cylinder go down just from getting gas? Mechanics so do they really know what is going on or just making guesses can anyone diagnose the problem for me im a certified mechanic tune-up specialist and I can't figure this one out help from anyone id appreciate it other than that the car has been an excellent running little car