Im leaning more towards a vacuum leak. I replaced the MAF this weekend. It still idles rough and will die If you rev it up and let off the gas. I also started to have gas fumes come through the vents. I read on another forum that gas fumes with the rough? dying idle is the MAF. But I swapped that out and no changes. Any ideas? its a 2006 f150 5.4L. Thanks

 

Gas fumes could be leaky/stuck injectors.

 

I had gas fumes coming into my 06 truck about a week after the dealer put a new engine in it. They found a broken fuel pressure regulator, actually I think they used the term "cracked".