The EGR valve on a VW TDI recirculates the exhaust gases back into the engine for a more complete burning. EGR valves are an emissions control component designed to reduce emissions into the atmosphere. However, the EGR valve on the VW will get dirty over time due to carbon deposits. You'll feel this when the car is idling because it will idle very rough. When this happens, it may be time to clean the EGR valve.
Turn the EGR valve upside down onto a flat surface.
Spray the EGR valve with carbon cleaner. The cleaner is a very powerful solvent that will remove most, if not all, of the carbon deposits inside the EGR valve. Spray the EGR valve liberally and fill the valve up with cleaner until it is spilling out over the edges of the valve.
Allow the valve to soak for 12 hours.
Dump the carbon cleaner out of the valve.
Clean any remaining carbon deposits off the valve with a small wire brush.