smartbomb

I have an 04' SL500 with 80k mi, rear muffler delete, and k&n filters. My check engine light came on so checked gas cap. I've been through numerous ign. cycles still on. continued to drive, experiencing no running problems, until now. started normally, after pulling away, noticed a misfire and CEL started blinking. Misfire went away quickly, but reappeared several more times until engine warmed up. Had the OBD scanned, and it detected the misfire in cyls. 5,6,7, also a random misfire(0300), and also air injection system fault (0410). I know I will have to take it in, but my local "stealership" is fairly shady, so I would like to go in as knowledgeable as possible. If anyone is familiar with this, your input is greatly appreciated