afr problem

[djl601]

hi,
i have a s13 with blacktop sr and some basic bolt-ons, FMIC, SAFC, and aem wideband gauge, and also openair

when i cold start the car, it will give me around 13.6 for maybe half to one min, then it goes down to around 14.6-15, but when i'm driving, whenever i let go the gas peddle, the gauge will show me " --- " which means over 18 afr

what might cause this problem? and how can i adjust it from my safc?

i was going to do a dyno tune, but a friend of mine to me it's a waste of time and money on dyno tune a car with nothing but a SAFC! what do you guy think?

I'm also looking for a Apexi power fc, but wondering if i really need it now for a basic set up like mine. my goal is to get around 300 whp, but that's not any time soon.

basic setup sr20 + apexi pfc = OK?

thanks