Have you resoled your problem? I had a 300ce that had a mechanical vacuum pump located in the front of the engine. The pump was driven by the intake cam, this pump had a diaphram that failed and caused exactly the symptons you described. The power booster to the brakes used the boosted vacuum for power and the busted diaphram caused the engine to smoke because the pump had one like to the booster and one line to the manifold. The line between the pump and the intake manifold was clear plastic, when the pump failed it allowed oil to flow into the manifold and the clear line turned black. I purchased a diaphram for like 20 bucks and fixed the problem. If your car has a mechanical vacuum pump give it a check. Take care and good luck!