Der E32 stinkt :-(

[Erich]

Weisser "Qualm" ist ganz normal, speziell bei diesem Wetter und wenn er nur ab und an richtig heiss gefahren wird. Das ist Kondensation im gesamten Auspuff, der muss einfach mal richtig warm gefahren werden ueber 50 km und mal richtig heiss werden, damit das ganze Zeug innen mal wieder trocken wird.
Nicht umsonst sagen sie in USA zum 750 im Winter "Nebelwerfer".

Zu dem Thema verfaulte Eiergestank hatte BMW mal in USA extra eine Technische Info rausgebracht, auch Audi, hier mal teilweise kopiert:

ROTTEN EGG SMELL FROM CATALYTIC CONVERTER
The sulphur smell from the exhaust, is actually caused by running the engine/cat convertor slightly lean for long periods and then running under a rich condition (ie going up a hill under heavy load) This is when the sulphur smell (rotten egg) is produced.
Under relatively lean conditions, the sulphur found in gasoline is converted to sulphur trioxide, then during the rich running condition the sulfur trioxide is converted into hydrogen sulphide (rotten egg smell) within the catalytic converter.
Audi of America issued a service bulletin Group 24, #92-04 which detailed this problem. They list the cause as : the gasoline sulphur content and the characteristic of catalytic convertor to store sulphur compounds and release them during rich engine running conditions.
Switching gasoline brands may help. The Oxygen sensor may also need to be replaced to correct a fuel injection mixture problem.
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Rotten egg smell- not a defective cat (von BMW)
On some vehicles, a sulfur smell or 'rotten egg' odor may be noticed coming from the exhaust system. The odor is usually noticed after a cold start, fast idle, extended periods of idling and full throttle acceleration. Sulfur smell is not an indication of an engine concern and will not cause reduced driveability or durability of the engine or any of its emission components.
The sulfur smell or 'rotten egg' odor is caused by high amounts of sulfur in the gasoline being used in the vehicle. Sulfur is normally eliminated during the refining process, but the EPA regulation of sulfur in gasoline differs from state to state. Vehicles using fuel containing high amounts of sulfur will most likely emit sulfur smell from the exhaust system.
When high sulfur fuel is burned, there is a chemical reaction in the catalytic converter causing the sulfur to oxidize. As the vehicle is driven, the oxidizing reaction odor in the converter will decrease with mileage and age. Replacing the catalytic converter will not eliminate sulfur smell and replacement will just extend the period of time needed for the converter to 'age' allowing it to reduce sulfur smell to an acceptable level.
1.Switch to a different brand of fuel and drive the vehicle for at least 100 miles. Monitor the decrease or increase in sulfur smell.
2.Do not add any type of 'fuel additive' as this could add sulfur to the fuel and cause/increase the odor.
3.Try to avoid extended periods of short trip driving or aggressive acceleration.