Sometimes, a misfire, sputter, poor acceleration or rough idle can be as simple as water in the fuel tank. Some water in the tank is normal but more than that will cause a problem, sometimes more so when you let the tank run low. This could happen when you’re filling up at the pump or from condensation. If the car sits unused for a while, water will sink to the bottom of the tank where the fuel is normally drawn from to run the car. So, before you go to the expense of changing plugs or coils and so on, if you have reason to think it might be excess water, drain and refill or use an additive to get rid of it. Note the latter won’t work if there’s too much water in the tank.