"Missing" means that one or more of your cylinder is not firing right and/or not firing at all. Usually, when "missing", the engine shakes at idle, and if you have more than one cylinder "missing", the shakes usually won't go away as you accelerate. "missing" won't cause any damage, just that fuel goes in, and comes out without completely burned. And if your engine is "missing", and there's smoke comes out of your exhaust(black, look like from desiel cars), it's ok. Those black smoke is fuel that isn't burned, and comes out from the exhaust.
White smoke(or Blue smoke)mean Big$$$. The engine oil is some how getting into the engine, compress with air/fuel and burned with. If you have White smoke, take the car to dealer ASAP.
P.S. I just have my cap and wires changed, because my '92 400SE was "missing", too. I have 4 cylinders not firing at all(ya, it drove like a Lada by that time), and some black smoke would come out of tailpipes if I accelerate(not always, smoke would gone if engine is at working temp. about 86C) So, go have your distributor caps check, and make sure all ignition wires/spark plugs are in good condition.
Hope this helps....