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P0171 System Too Lean - Bank No. 1.
With the work already done, I suggest that you clean the MAF sensing element and check for vacuum/intake leaks.
Several techniques for MAF cleaning to be found with a search.
Air leaks can be caused by a loose or missing dipstick or oil cap. Leaks at the PCV valve or fresh air tube are fairly common. The PCV valve has a short rubber hose under the exhaust manifold that becomes affected by the heat.
If it is not affecting driveability yet just start ruling these out.
