I had this same problem when I ran my new setup on my car. LTFT's were at 16.4 at idle or when I let off the throttle, with what I thought to be "no vacuum leaks." I searched forever and ever and couldn't find one, and I leaned towards it being my tune as well. After spraying enough brake cleaner/carb cleaner, I found the TINIEST leak in the throttle body. Small enough that it didn't even affect my AFR's at WOT, or my vacuum/boost number at idle or WOT. I know you said you checked already, but I'd double/triple check for vacuum leaks. It's rare that our cars show 16.4 LTFT's without a vac leak present.
