I have a Ford Windstar and it keeps on showing the trouble codes p0171 and p0174. When I checked the van, I noticed that I could pull the PCV hose out without any resistance and also that rubber grommet was soaked in oil. I shaked the PCV valve and it rattled. Also when you are driving the van it hesitates when you hit the gas and sometimes at a stop it feels like it wants to choke out and die.
Ford makes a kit for the pcv, hose and fittings. It includes the valve cover as well.
As far as the codes, it could be vacuum leak, maf sensor, fuel pressure or pcv. A shop with a scan tool can monitor long term trims and use a smoke machine to find the source of any vacuum leak.