These are starting to pop up again at our dealer and decided to show what the concern is all about and how to fix it up step by step. The check engine light will set but you may not notice any performance issues. Hope this helps!

 

also from experience....for my 2002 Ford Windstar (180,000 miles) replaced isolator bolts 3 yrs ago b/c of lean codes...solved....P0174 and P0171 codes returned AGAIN last yr....replaced lower manifold gasket....solved......P0174
& P0171 return AGAIN this year....i thought is was a vacuum,leak...it wasnt.....old MAF showed continuity so I thout it was ok....cleaned wit MAF cleaner...still showed codes....replaced MAF with this part.....SOLVED...no more lean codes...

 

Yep those are the 3 most common sources for sure on these.