87'5.0

What all is involved to switch from efi to carb. Is it as simple as changing intake manifolds or is there more to it?

Ipaman

Mine has been changed over. The previous owner installed an electric fuel pump. Not sure if it was needed but it might be something you look into.

88 orangepeel notch

You can find out all that's required if you use the search feature here and dig up some old threads that cover this start to finish. But I'd still investigate your situation first. It could be as simple as a split vacuum line. Don't give up on the EFI just yet, there's a reason carbs are outdated.