Archangels

when i first start my car it will rev and idle nicely however, every few seconds the rev's take a dip and at times the car almost dies, at idle the car runs around 12.9:1 AFR and when it dips it's seeing 16+ AFR, when the car is all warmed up and ready to go it idle's like a champ, but until then it's bitchy....

any idea's as to why it would do this?, i have an S5 with large street port, BNR3 turbo, ported intake manifolds, power FC and a knife edged throttle body with the secondary butterflies removed....

it idled alright once it was tuned, but now all of the sudden it wont....