This appears to be a common problem!...I also have a 1998 Expedition EB 5.4L Triton (77k miles), and have a rough idle and "check engine" light warning. I just wanted to thank you all for this forum and great ideas that are shared. I am headed to Autozone this afternoon to see if I can get a code check to determine if I need to replace O2 sensors MAS, or a PVC valve (haven't inspected this yet).

The thought of taking my truck to a dealer and paying through the nose to fix this problem lead me here (that and the realization that I was looking at 4 O2 sensors to troubleshoot!). I appreciate the info that you all provide!

Question: Are the O2 sensors hard to get at/replace?