In the pictures below, the tube in question is seen to be connected to nothing at either end. It seems to me that it has something to do with intake. What is it and how important is it? It also seems that the engine could go for a healthy cleaning. The contrast between the spark plug wires and the valve cover has me suspicious, and it looks like it might have either a valve cover gasket or head gasket leak. Exhaust manifold and O2 sensor look to have seen better days.