I have a hose that runs from the passenger side of the intake manifold, behind the engine to a piece on the firewall near the master cylinder. It appears to have a join in it directly behind the engine and I think it is suspect. I wanted to replace the line, but was unsure how to remove the connectors on either end, or what the hose is for.

I have an 04 FX4 5.4 and as far as I know it does not have a PCV valve. I could have just taped the connector back up, but I wanted a more permanent solution.

I swiped a couple of photos from another thread of the line in question.

 

That's a main vacuum supply line for all that stuff over by the master cylinder. Not sure how to take those connectors apart, though. I'll be watching.