In 2004, Audi A6L 2.4 V6, the throttle was cleaned, the spark plug was replaced, the three-way catalytic converter and oxygen sensor were replaced, and the exhaust gas was still heavy.

Dear, I suggest you measure the cylinder pressure, because your throttle has also been washed by volcanic flowers and replaced by three-way catalysis, and all oxygen sensors have been changed. If the tail gas is still heavy, I suggest you look at the cylinder pressure and see how it works. There may be something wrong with the seal of that engine. I hope the answer can help you.