Vacuum leak

I recently discovered that my car blew a spark plug. It melted part of the valve cover so I had to replace it. I also had to re-thread the spark plug hole, which is still suspect because the kit I bought at AutoZone had a tap that made the hole too big. Anyway, once I "fixed" the spark plug issue, I decided to smoke test it when the check engine light came back on after driving for about 10 miles or so. Didn't see any smoke for a bit, until it started coming out from behind the driver side headlight. I can't see back there but was hoping that somebody knows if there is a hose or something that runs back there that I would need to check or replace.