so i get my car tuned and for three weeks its running great! but then one day i was driving back from the commissary and the car started to go lean while cruising; around 17-18afr and then maxes out(- - -) on my aem afr gauge. i made it home trying to keep the afr's stoich. NO CELs. shut her off and tried to start her again. didn't start. crank turns and battery is good. after approximately 15 minutes later, i tried to start her again. it took one looong crank and she started, but it was weak. idle afr was normal, but when i tried to drive around it would lean out again! and also it would have trouble starting. the tuner mentioned that one of the o2 sensors was acting funny, but i'm not getting a CEL. what the heck could it be?!

2003 350z
APS ST
walbro pump/650cc injectors
Osiris

i do not have cipher. my tuner installed the license and started tuning. he said it doesnt come with it.

 

Did you call your tunner