My Mazda Millenia Is giving Code P0300 and P0173 and I need specialize in premium Japanese and German imports to fix it for me in a reasonable price

A fuel trim malfunction can result in random misfire and random misfire can sometimes register as a fuel trim malfunction due to how the ECM processes fuel trim feedback. So, I'd start looking for air leaks from bad or misrouted vacuum hoses since that's the more likely culprit, then move on to troubleshooting the fuel system.

Of all the possible causes for both codes, these are the more likely ones (in no particular order):

Fuel pressure regulator control (PRC) solenoid valve malfunction
Fuel pressure regulator malfunction
Purge solenoid valve malfunction
Spark plug malfunction
Coil malfunction
MAF sensor contamination
Vacuum leak between MAF sensor and dynamic chamber
Purge control solenoid valve malfunction
EGR valve malfunction
PCV valve malfunction

 

May I suggest to do an Internet search for Japanese automotive specialists in your specific area? e.g. "Japanese automotive specialists, Stanford, Ct." and see what you get.