ok so i keep getting troble codes p0420 and p0133 and i keep erasing them with the old disconnect the battery trick . eventually the codes wouldn't erase . so ibought a code reader and it erases the codes no problem . also i seem to have alot of backfiring on deceleration and it seems the codes come on during the bacfiring or so it seems.i know our cars are supposed to pop a lot with full exhaust but the clap off some of the backfiring just dont sound healthy. does any one know how to correct this is it just timing or would there be an error code for timing problems cause the above codes are exhaust related. any insight would be much appreciated!