UK Car Repair: egr valve, vauxhall combo van, vacuum pipe

Question
vauxhall combo van 2003 1.7 turbo diesel it was blowing a lot of black smoke out especially at 3200 rpm and was getting slugish took it to an expert he took off the vacuum pipe to the egr valve it goes very well now after a few miles blowing soot out of the exhaust but that is not the answer what can be wrong with the egr valve?

Answer
How many kilometers are on the car? Did the mechanic leave the tube off or replace it, and, didn't he say what the problem was? The egr is supposed to take some of the exhaust gases and return them into the cylinder with the object of burning off more of the pollutants. It usually provides maximum flow at high RPM. There is no vacuum to it at low engine speeds as the combustion process is not capable of using it efficiently. If the engine is worn out there may be a very high level of unburnt fuel, this then mixed with the re routed gas is causing a higher level of unburnt fuel exiting the exhaust.