My 1991 350SD when started in the morning coughs and emits large clouds of blue smoke. It is even worse in cold weather. It stops once the car has warmed up.

Mercedes technicians have replaced the fuel injectors, fuel filters and timing chain. In addition, they have checked the glow plugs. Nothing has corrected the problem.

Does anyone have any idea as to the problem and any suggestions as to how it can be corrected. Thanks.