Toyota Repair: 2000 toyota celica gt random misfire, mass air flow sensor, mass air flow

Question
i have a 2000 toyota celica gt the engine is a 1zzfe it has a random misfire the check engine light is on but the only code it is throwing is p0300. i can not isolate the misfire to one cylinder. i have cleaned the mass air flow sensor, there is no intake leak that i can tell, my headgasket is good, and i just replaced the cataylic convertor because it was clogged up. what are the causes for a random misfire like this?

Answer
This can be caused by a malfunction that affects all cylinders, usually an intake leak, mixed up vacuum hoses etc.however, Toyota had published a service bulletin that addresses this condition,TSB-
EG003-01, it involves replacing the ECM and the fuel injectors, if you would like a copy please let me know.