car idles good but when you step on the gas pedal, the car is very jerky and wants to die. I replaced the fuel pump with a Carter and it stills does it. Has a reproduction coil and starter solenoid. The mustang starts up fine and has a 1/2 tank of fuel. The mustang is a 289 with a 4 speed. The car was running good one day and then the next day, boom. Any ideas?