need a tune up for sure but wondering of any else on 1998 Lincoln Navigator

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truck has 185,000 miles an needs a tune up bc the chk engine light was chkd an 2 codes refering to the lean system on both codes. been told oxygen sensor possibility an spark plug need change along wit tune up. misses a little when is started on occasions but never shut off. barely flutter on times.
(2) Answers
I'm guessing the codes are P0171 & P0174. You have a massive vac leak. Most likely at the rubber elbows or rubber hoses going to the PCV valve.
Quite frankly I would replace both upstream O2 sensors just for preventive maintenance.
When was the last time you changed the spark plugs. If you decide to change the plugs make sure you also change the rubber boots between the plug and coil.
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