What's causing error code 300? Check engine on but later on will disappear. on 2002 Mazda Protege5

Check engine will start blinking every time I go faster pass 60 mph or when trying to accelarate faster; the check engine starts blinking and will lose power, just wouldn't go even if you step on the gas. My mechanic does not have the interpretation for the code, saying need to bring to the dealer,(which will cost me arm and leg).

Asked by for the 2002 Mazda Protege5
sounds like a mis-fire