Rocketbunny240sx

Hey guys my sr20det redtop in a s13 hatch has been running extremely lean out of no where it slowly got there. My afr gauge used to be at the 14-15 range then it went to the 16-17 range and just today went to 19 and 20 the gauge even saids lean once a while now. When i boost it, it runs fine it will boost away no problem. I thought it may have been a boost or vac leak some where cant seem to find any. And i just had new plugs gapped to .32. Ive got a supra twin turbo fuel pump 390lph and i have 750 cc nismo injectors. My fuel pressure is set to 40 psi. Im also running a fuel management system so no iacv. Need help anything works! Thanks!!

I forgot to say it was only at idle it leans out. It will go from 14 ish and then all the way down to 17-19