Q: White smoke at idle, oil residue on engine

Hello. From the symptoms you describe, it would appear that the vehicle has some sort of issue with the cooling system. If the white smoke was coming from the tailpipe, the coolant has to be frequently replaced, and the there is residue in the oil, then it may be possible that the engine has suffered a blown head gasket. This is likely the case if the vehicle has experienced any severe overheating, or has accumulated a high number of miles. If the leak is small, it may not be enough to cause the vehicle to overheat, however it may cause white smoke to be produced from the tailpipe if any coolant is ingested and burned by the engine. A thorough inspection should be conducted in order to determine what exact problem it may be.