I have recently Snapped one of the lines to my Exhaust Gas Re-circulating (EGR) Valve whilst playing about with my airbox by accident. Not knowing exactly what I had done I took the part number from the item and phoned audi to ask them to not only order me a new one but to tell me what it actually was and the implications of driving the car with it damaged. They told me that they had ordered one for me and that it was called an EGR solinoid valve with no explanation about its purpose etc. Bunch of muppets at audi I must admit however to cut a long story short I have now replaced the valve and have noticed an incredible difference not only in power increase but fuel economy (about 5-7 mpg more). After fitting it I came to the conclusion that my original valve was faulty in the first place as it has never driven like that in the 8 months I have owned the car.

P.S If you wish to know the technical aspects about the EGR valve and system just type it into any of the main servers and you should find a good site explaining their functions.