Rough I park and growl when I accelerate

So I recently replaced the battery on my 2007 Mazda 6 (3.0 engine). A day or two later I got a running lean code. Didnt have time to fix myself so took to my mechanic. He found the intake boot cracked close to the MAF sensor. He relaxed the boot, code gone but idle still slightly rough. Noticing a growl when I accelerate. Mechanic (who is an honest guy) says he thinks I may need a new catalytic converter but since I only plan on having the car another 6 months its not a big deal if I dont replace. I drive for work and cant afford to have a major breakdown. Isle RPMs around 750. When its idling it almost feels like a slight sputtering from the exhaust. Any help would be greatly appreciated.