P0171 and P0174 on 2005 X3

[Fandu]

I went through many posts regarding the 2 codes. 3 years back I replaced the boot and the car ran fine. Then last year I had white smoke coming from exhaust and ended up replacing the valve cover and gasket which fixed the smoke but then started getting the dreaded p0171 and p0174. Replaced the CCV and DISA as well.
Did a home made smoke test and no leak. Thought there might be an issue with my home made device so took it to an Indy for a professional smoke test. Nothing no leaks.

Trying to figure out what to attack next - spark plug, O2 sensor or MAF or anything else I may be missing.
The car has 136k miles and spark plugs were replaced at 86k miles (6.5 years ago).

Any help is appreciated.