2009 Chevrolet Cobalt - Cobalt ls project

First mod car. 2009 Chevy Cobalt Ls coupe 5-speed. Future mods: cat back exhaust, new COI, headers, tune, front strut bar, lowering kit, tint. \nLosing MPG after intake installed. Stock 30-34 mpg. Now getting 23-25 mpg. Any ideas as to why? Would a tune h