I have checked many threads and cannot find quite the same thing as I have. I have a 2004 Ford Focus ZTS with a 2.3L 4 cylinder engine and a manual transmission. The only way I can think to describe what the car does is that it "chugs" or possibly "jerks." The car starts just fine but it's like the engine isn't getting enough fuel all the time. I have replaced the fuel filter and the spark plug wires (not conventional wires) and the problem has gotten a little better. Also, the "chugging" gets worse when the AC is on which is why I think it's fuel related. Before any repairs were made, it was bad enough that I couldn't always get the car going from a stand still without revving the engine significantly. Check engine codes were multiple cylinder misfires, cylinders 1, 2, 3, and 4 misfire before first 1000 revolutions, catalytic converter, and O2 sensor. Does anyone know what this could possibly be? Engine gaskets, fuel pump, fuel injectors...?