It depends.
Going rich on decel is normal because you are cutting the air off before the pcm cuts the fuel. Best just to tune your WOT fuel curve by adjusting the MAF transfer function until you are in the recommended limits and then let the computer take care of everything else.
For no issues, no controversy and ultimate safety you can go for 12.7:1 A/F all the way across the board.
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black
