2000 Volkswagen TDI intake manifold

I'm a little confused? why would you want to clean your intake manifold? I own a half-dozen Jetta diesel's and I love every one of them and their intake manifold's are dirty but that's just what a diesel does, if you clean it it will just get dirty again, just because it looks black does not mean it is dirty And you have to clean, is your jetta experiencing some kind of problems? I have a 1981 Volkswagen rabbit since it was new and I have never cleaned the intake manifold and it is very black but it runs like a champ.