Lack of power - 2002 Volkswagen Jetta TDI

Very common with these engines. The EGR valve is built into the throttle body and allows for heavy carbon build up which starts to close the diameter of the hole. The only true way to repair this issue is to remove the intake manifold as a whole eith the throttle body and soak it over night with a good cleaner/solvent. It will take you scrapping out a lot of the carbon build up with a screwdriver/scrapper. Once this is done, this will run like new again. I have done a lot of these and seen the results. If you wish to verify what I am telling you; remove the air duct to the throttle body, open the throttle plate, look inside with a flashlight and you will see the black charcoal like restriction I am talking about. Let me know if you a need a shop manual.