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I have a 2003 Expedition 5.4l Eddie Bauer, 2WD.
My car became sluggish, and my gas mileage dropped down to 12.4city/12.8 hwy. Eventually the check engine light came on. I was pulling a P0171 code. I found the elbow attached to the PCV valve cracked. I replaced that, and the PCV valve as well. I cleared the code. Within ten minutes of driving the code came back. Gas mileage went back up some. 13.8city/14hwy. Continued to check the hose line and connections, everything seemed good. Went to check MAFS and found the entire seal around the air filter has gave way. Replaced using part warranty, cleared the code, and now it's back to normal! Gas is at 15city/16hwy. Not bogged down at all and finally takes off well again!! So happy.