...firing) code p 0300? i changed spark plug.injectors.fuel pump .the problem still misfiring

If you know what cylinder you are having a misfire in, try changing your spark plug wires between two different cylinders. (i.e. - if cyl 3 is misfiring, swap wires to cyl 3 and 4 AT BOTH SPARK PLUG AND DISTRIBUTOR and see if the misfire follows the wire) If this occurs, you probably have a bad wire.

It might just be a good idea to try replacing the wires anyway, they don't last forever and they're pretty cheap. I hope this helps you out, good luck! :)