When I got the alternator I was at 13-14 voltage. They have warranty so you can always take it back and get another one. I think it has nothing to do with the afc. On the 1g that I replaced the alternator I had the afc2 and voltage was fine. Something is up with your alternator it seems like. Are your lights dimming in and out?

Or I may be wrong... could this be a sign of idle surge? Eh, still lost on whats going on. But I'm trying to help.