Hello, I have a 98 Expedition with about 98K miles. 5.4 L 4x4. About a month ago I got a CEL and now the truck is running rough at idle and during accelaration at times. Got it scanned and the codes P0171 and P0174 (System too lean banks 1 and 2) I have read other post and understand that it's likely not my o2 sensors but something else causing this problem. I checked for the infamous leak at the 90 elbow but found none. I replaced all my plugs, boots, oil w/ filter, air filter, fuel filter, PCV valve and still have the problem. Can anyone please help with some advice as to what else I should look for. Thanks

 

Welcome to the site!

You already have a good response in the Expedition forum and I think you will find a lot of help there. Look around the site a bit and be sure and stop in your state chapter: https://www.ford-trucks.com/forums/forum186/