I'm new so take it easy on me. Was wanting to know what would cause this to happen and do I need to replace. I actually just replaced plugs and afterwards got a rough idle and low rpm. I have double and triple checked everything and can find nothing. Would this cause my problem? It's an 2004 f 150 4.6

 

Any codes? Maybe a vacuum line was loosened and is leaking?

 

Yes the notorious p0171,p0174 and p0208. Would a vacuum leak cause that crack?

 

P0208 is #8 injector code

 

What would cause this to crack like that?

 

And looks like something has been running out of it.

 

Can you back the camera up and point to the close up?

 

That's the best pic I could get it's pretty tight back there

 

What shows is just casting flash. Not a crack unless it does not show in the photo.
171/174 is an vacuum leak that has shifted the long term fuel tables for both banks.
Code 208 is likely an injector connector not seated since you just worked on those areas.
Good luck.