dgot

I owned 96 Impreza.It misfire on my way home.I do not know what's wrong,for I just change the battery and alternator,so I read the fault code with my Ms509 OBD2 code reader and it shown P0328, P0340, P0420, P0031.What's the code?Is it easy if I repair myself?

I need a diagnostic tool to read fault code and clear code,can reprogrammer is best.Someone told me U581 OBD2 Scanner.I want to know if it can meet my demands?