Just had my LTs, y-pipe, and catback installed

[bberretta]

Start by clearing the code yourself, fix the vacumn leak, and then running it again to trip the code- that way you're getting a clean set of codes. I don't think a vacumn leak would focus on a specific cylinder- that's got to be either injector, plug, plug wire or coil- I think.

[Too Fast]

I got my car back today and when I started it at the shop the engine light was on. I figured they deleted the codes. There was no rough idle like before and no cylinder miss that I could hear. Almost all the way home then the engine light came back on and I started to hear the miss but the rough idle didn't come back. Once I got home I scanned the car and only the p0306 code came up. My question is do I still have a vacuum leak and will the codes come back or are they gone for good?

The short answer is yes, most likely you still have a vacuum leak. Lean codes take more time to set, usually, than a misfire code. It is possible that you have a mis-diagnosed injector, and the vacuum leak is mostly at/near #6 injector. I would swap #6 injector with #2 and see if the misfire goes to that #2 cylinder. Also, it would be a good idea to fix the misfire code before looking for a possible lean code, it could be a bogus code since #6 is not firing.