Of course that happened. Because you opened up the engine to breath better, without tuning it. It's going to happen. You need a tune to fix it. No worries though, it's not going to kill your car. I've never tuned mine, while running a Cosworth CAI, F2 header, and Roush exhaust. Of course mine is running lean lol
Actually just removed the Cosi and did the DIY before I hand it over to the dealer tomorrow (traded it on a new Mazda3). I've got to admit, this looks good and nearly stock. I'm proud of myself. Cost me $24 for a Spectre filter at Autozon, $3 for a hacksaw from walmart, and $4 for a rubber gasket-type thing from Lowes to seal it up best I could between the inlet and the filter, as the filter only goes so small as a 3" inlet.