You don't want to use the aftermarket PI intakes with the built in gaskets to do the NPI head to PI intake swap. It doesn't work well, I wouldn't have guessed you would have huge unmetered air leaks, but that is exactly what you have, from the hiss and the lean DTCs for both banks.
Does it have ABS? I would guess vacuum leak someplace, could be your hiss and maybe causing the above symptoms, and you don't have an intake air port leak, but I have never seen anyone with any luck with the aftermarket PI intakes on NPI heads.
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00 Grand Marquis LS/Vibrant White/Gray velour
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