
You said that smokes pours out of the car when started & then dissappears. This can be valve stems seals. When the car is switched off the oil leaks through the seal into the combustion chamber. When you start the car, the oil gets burned which is the smoke & dissapears as all the oil is burnt off.
I also was speaking to a guy from porsche & he mentioned that you get a puff of smoke everytime you start a porsche as porsche has designed a turbo that leaks oil out of the oil seal in the turbo when switched off. The reason is for protection when the engine is started again that their is oil on the bearings already even before the oil pump can get to it. doesn't make sense to me, but that is what he said.