hi all, i have a 2008 sprinter 312 ,4800miles on clock, it is used as a mobile workshop carrying out repairs on cranes, i have an automate welder generator system which requires the engine to be run at approx 2000 to 2500 rpm to get the required green "ok" lamp on to carry out welding, grinding etc, i have the problem that after i have finished the job and drive away the engine runs very rough for a while and completely covers the road behind me with white smoke, this clears and then runs beautifully again until i next have to have the engine idling when attending breakdowns at night and require my beacons/worklamps on or carry out more welding/grinding at 2000 to 2500 rpm, generally this happens after it has been running stationary for more than 1/2 an hour, any suggestions as to cause as my local mercedes garage are being there normal helpful selves and dont seem to care. many thanks scott