My '92 300D with 200k miles on it starts up with just a touch of the key. Given a good glow plug cycle of 15-20 secs the car roars to life and idles wonderful - for about 3-5 secs.

After the first 3-5 secs it sounds like one of the cylinders is missing and it coughs a bit - spitting out white/gray smoke.

After about a min or so of this the engine purrs like a kitten again and all is good.

This only happens when the engine is cold. Glow plugs were just replaced and tested (resistance readings were within spec).

Any idea what this might be?

Thanks,

-John