Car runs lean at idle 4-5 seconds after starting
I just noticed that my car is running around 15-15.5 AFR at idle and constant throttle. The weird thing is that when I first start it up it runs perfect for 4-5 seconds then my AF's go insane and start bouncing from really rich to lean and the finally settle at the 15-15.5 area. Also sometimes it will get worse and hit 16 at idle every now and then.
Ive checked for exhaust leaks, also have no boost leaks, my mods are
Apexi SAFC Neo (which I turned off and it still did the same thing)
Greddy Type-S BOV
Does anyone know what could cause this? I don't think its my wideband because I can feel the far react to the big lean spikes. I'm thinking of replacing the upstream o2 but I wanted to get some input before that.