I just bought a 1977 300d with 51,000mls. I live in Denver (5280feet-thin air). On mornings when the temperature is around 20 degrees and I start the car, I glow it once or twice. When I start it, it begins to fire on a couple of cylinders and I need to keep the starter engaged for about 10 or 15 seconds for it to hit on all cylinders. Is this normal or should I work on it until it hits on all cylinders immediately? I have adjusted the valves and checked the voltage on the glow plugs. They are all getting voltage but they are in series and the last one reads at about 1.5 volts. The first one reads 10.25 volts through the plug.
It seems to start best if I give it little or no fuel with my foot.

It sounds like you could use new glow plugs and possibly some work on the gp relay. In the owners manual it does say that you can keep holding the key in starting position until the idle smooths out, so I don't think you have too much of a problem there. The starters are designed to take the extra abuse from getting a diesel going. I'll let the other more knowledgeable members answer your question more completely. Hope this helps!

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Sean Roland

2004 Saab 9-5 AERO 138k (for sale)
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