I had your exact problem on my boosted TA in complete open loop MAF only tune....it was the charge temp blending table. When the engine was warm the car would lean itself way out. If I let it sit and cool down it would go back to normal. It would go LEAN when WARM and RICH when it was cold out, exact opposite of what I expected. I moved the charge temp blending table to something more ETC based than IAT based and the problem went away.