engine sputters at 1200 to 1800 rpm when shifting on 1999 BMW Z3

Engine will sputter when I shift gears. Code P0303 was stored. I replaced the coil but problem continues. I switched the spark plug and ignition wire but it continues.

Asked by for the 1999 BMW Z3
Try swapping the injector to a different cylinder if that's possible. Check the compression of all the cylinders, and make sure there are no vacuum leaks or EGR problems.