http://986forum.com/forums/general-discussions/51323-random-starting-issues-cel.html
I had the same code come up and thought it was unrelated to my starting issues but also had bad readings on both oxygen sensors (those ended up being from the AOS failing). The P0446 for me was the regeneration valve from the charcoal canister to the throttle body not working correctly. I bought one from the dealer for about 133 dollars. It's an easy job but a lot of work in tight spaces. I would check out the threads on hot starting issues to see if that sounds like your problem. Replaced mine for the same code you have and it has not returned for at least a couple months now and no starting issues.
I do want to mention though that my car would always start, but if it was within about 30 minutes to an hour after I last drove, it would give me trouble and I would have to give it throttle and try a few times. It started getting more and more common before I replaced it.
Good luck!
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