there isnt any point in plugging it. its connected to a metal shroud that has 3 bolts that literally just sit ontop of the exhaust manifold. there is nothing to do with the vacum if you disconnect the long metallic tube. Most of the time they end up just rotting away. Now if you disconnect that little black vacum line on top of the intake ( the filter box to be exact ) then you will have a leak and then you will have problems.
the tube from the manifold to the intake isnt really neccessary, and if you were to replace the manifold with like a ranger manifold it has to go anyways, so dont worry about it, if it looks bad get rid of it. If you really want it, go to autozone with the tube IN HAND so you can visually compare to see what you want for a new hose. called a preheater hose btw, at autozone