Back firing

i had three trouble codes. one was multiple cylinder misfire, maf sensor low output,and knock sensor low output. I changed the MAF sensor and i erased the trouble codes. one trouble code appeared again, it was multi cylinder misfire. I changed the spark plugs and wires. but before i done all of this, the truck idle was erratic, it was missing, and backfiring. now itsz running smooth, but its still back firing.