Friend of mine is transplanting a 300tdi engine into a 89 110. Going well so far but we've come across this pipe in the engine bay, it is a small pipe that Tees off from the main pipe from the vacuum pump to the brake servo and goes right across the engine... (When finding the same pipe on my disco for reference) What is it? What does it do? How important is it? Pics below

disco uses vac to operate egr

Thanks !