If there really is White Smoke at sometimes; as said previously Coolant. But, I have also read White smooke can be Atomized unburned Fuel.
If you having the White Smoke at idle take a piece of Card Board and hold it near the Tail Pipe for a bit.
If it smells like Diesel Fuel you need to investigate why it is not burning.

Also there was no mention of doing the Injector Cutout test to locate a possible Cylinder that is causing the problem.

Maybe the Idle speed it too low for the SLS.

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84 300D, 82 Volvo 244Gl Diesel