RX8 backfire issue

I finally got my 2005 Rx8 manual tranny running but it backfires, i will be changing plugs,wires and coils in the next few days, can that solve the issue? It backfires if i rev to about 3000 rpm when idle or when i hit 2nd or 3rd gear. Could it be bad injectors? exhaust leak? If its an exhaust leak is expensive to repair. Any info is appreciated. Thanks