When I start my '83 300D after it has been sitting overnight, it starts right up and runs smooth for probably three seconds before it starts to miss a bit and expels a fair amount of grey smoke. It will do this even if it is 80 or 90 degrees out, but it gets worse as the temperature falls. Unless it is REALLY cold (i.e. below 40 - that's really cold for Houston), the problem goes away after 30 seconds or so.

If I let the glow plugs run a full cycle, the problem is reduced but not eliminated. That is, I have the missing/smoking problem even in August after a full cycle of the plugs, albeit not as badly as in the winter.

I replaced all five glow plugs in May (I used Bosch), which was about 22,000 (almost entirely highway) miles ago. I reamed out the glow plug sockets when I replaced the plugs.

I just removed all the plugs and hooked them up to 12V. After a few seconds they all glowed white-hot.

After that I tested the resistance at the relay, and all of the sockets read between 1.7 and 1.9 ohms. Based on other posts, shouldn't this number be lower, like under 1? And what exactly does it mean if every single plug reads high - that I installed five brand new but faulty plugs, or that the plugs are already wearing out?

Oh, and the valves were adjusted around 6,000 miles ago. I did it myself and am confident in that I did it correctly.