The plastic/replace with rubber tube referred to is the vac line supply from engine to Switchover Valves.[ common line to egr/air swo's and common egr code fault]
If one suspects blockage at egr tube , the simple test is to apply vac to egr at idle and watch for engine roughness. [egr is not normally energizd at idle]
If there is noticeable difference , than the tube is not blocked ..........