Tacoma,Engine is misfiring and Check Engine Light is on

Vehicle engine occasionally starts missing and check engine light starts flashing.It will last for about approximately 5 min. I have had it checked by computer when it is running right and it says misfire on number 3 cylinder. I replaced coil,oxygen sensor,fuel filter,and plug tube set.The vehicle still has the same problem. Changed spark plugs also.

My car has 278000 miles.
My car has an automatic transmission.