So my 2004 F-150 . 5.4 L V8 drives almost perfectly. The only issue I have is when I am cruising above 40 mph with a low idle, then slowly accelerate, a feeling of misfiring and exhaust vibration. Can a rusted exhaust/ muffler cause a misfiring? The check engine light was on with a PCV valve code and a lean on cyl 4. On this model the PCV valve is attached to the engine block so instead of replacing it, I took apart the hose, cleaned it and this other black part plastic piece that connects to the hose around the throttle body.

I am linking two videos that are of the issue while driving, and a video looking at the rusted out muffler. I think the Cat converters are fine.



Please help