A Strong smell

Hello, I drive a 1994 318i BMW Sedan with 195,000 miles automatic transmission which has a strong smell. I recently had a Air flow sensor intake replaced and since that replaced my car has been having a few strong carbon or exhaust smell. My brother take the car to BMW Motor work company who put a used air flow sensor on the car. The smell is so strong when I stop at a traffic light and when I park the car in the garage. I took it to another BMW dealership to see what was wrong. I told them about the smell. They found some loose bolts from the Steering rack which they stated should take away the smell. The smell is still there and it is making me sick. I suffer with bronchitis and any strong fume will start my bronchitis.