I have noticed a black carbon patch roght where my exhaust was, on the driveway occasionally. I had a decarbonising of my inlet manifold and redone the cylinder head in December. Could carbon have accumulated that fast in the engine within 4 months?

I normally drive only about 35kms everyday to school/work/home with my 2001 1.9TDI and hardly have the opportunity to push the car over 4000Rev for short distances. Is the short driving distance a cause of carbon and soot accumulating in the engine and cause for future problem?