The fumes will probably be down to one thing and one thing only. At the back of the engine, behind the cylinder head is a breather hose that comes from the crank case, made of rubber, which traverses a right angle on the near side of the engine to the rear. Over time this gets very very perished feeling all mushy, and eventually holes, filling the car with fumes which makes your eyes smart! My 90 had exactly the same problem. Audi sell a conversion kit whereby the rubber hose is replaced by two shorter hoses and a metal middle hose that carries the 90 degree bend. I bought mine from VAG parts when they were still in business.
It is a proper pain in the arse to fit but I am 100% confident that will cure it.