Is the only code P0303? Fuel pump would most likely cause multiple cylinder misfires. One cylinder misfiring on a 4 cylinder car is a pretty big deal and will cause a major decrease in performance. Is it still just #3? Have you checked continuity and resistance between the coil and injector wiring to the ECM as well as checked for shorts to ground? I know you said leak down was good but, did you check valve clearance? If everything is OK this leaning towards an ECM. Also, maybe even sway the new parts to different cylinders. New does not always mean good.I did every imaginable check on the engine, the leak down went well.. there are no torn hoses, new intake manifold gasket, new spark plugs, new fuel injectors, new coils.... so at this point i tried to drive it with its issues, i noticed that when i pressed the gas lightly the car would barely move then have a surge in power, also when i press the gas to take of from a red light it feels like the car is on a rumble road for 2 secconds, then goes back to normal, and the missfire/sputtering happens only at idle and i also noticed that the engine sputters alot when going about 50mph...it wont go any faster.... lastly the car has a serious lack of power, and some awful mpg (the least of my concerns).
can it be a fuel pump?.... i mean the car does have 250k miles on it