what causes miss fires in Altima 2003,also would a defective cat converter cause on 2003 Nissan Altima

coil 1 and 2 have been replaced, codes 042 and 300 keep coming up

Asked by for the 2003 Nissan Altima
seek diag and est as it could be several issues,a plugged catt would cause misfires and lack of pwr