I have a 1999 f150 lariat with a 5.4L. It recently started running rough at idle so I replaced the pcv valve and fuel filter. After replacing these it still ran rough. I took it up to advanced auto and and had them do a check engine light read and it said 3 of the 4 o2 sensors were bad. I replaced all 4 o2 sensors and it ran fine for about a day and the check engine light came back on. I again took it up to advanced and had them hook it up and now its saying its running lean. I am alittle stumped and to short on cash to take it to a shop. I had thought maybe mass flow air sensor but I am not really sure. I would greatly appreciate any help.