a few times recently i'v left my '03 320d idling, due to running a 240v power inverter or tyre inflator and not wanting a flat battery. when i come to drive off there is lots of smoke out the exhaust for a few mins then returns to normal. over the years leaving other diesels idling hasnt caused me any problems at all, until this car. so my question is - is this causing any damage? or am i ok to continue?