Re: 2001 windstar
If the codes are PO171 and PO174 there is a TSB on this and you have to replace some bolts in the plenum and possibly the left [front] valve cover. There are a lot of postings on this extremely common Windstar problem. I found the TSB info on Alldatadiy. I did it and the lean conditions came back. Then I discovered a cracked flex hose on the exhaust side allowing oxygen to enter the exhaust, fooling the O2 sensor into thinking "lean". Fixed the flex hose and error code never came back....