Since there have been a number of cold weather starting posts, it piqued my interest enough to go read what my Owner's Manual actually said. While I've owned diesels before, I am a vintage Benz diesel newbie. That said, this is for the 1980 model year. Whether or not newer 123's are the same, I don't know. Not yet, but I will
So for any newbie without a manual and were curious as to how MB recommended winter starts, I offer this:
With the engine cold, depress accelerator halfway and turn idle speed adjuster counterclockwise to the stop. Then release accelerator.
Turn key in steering lock to position "2" (run position). Charge indicator and preglowing indicator lamp must come on.
The preglowing process then begins. The engine can be started as soon as the preglowing indicator lamp has gone out. Since the glowplugs continue glowing for up to 1 minute, the engine can be restarted during this period without preglowing again.
Turn the key to the stop to start the engine. Release the key only when the engine fires regularly.
When the engine is at operating temperature (coolant temperature above approximately +70*C/+158*F), the preglowing indicator lamp comes on only briefly. The engine can be started immediately.
At ambient temperatures below 0*C/32*F and with the engine cold, completely depress the accelerator while starting. Actuate starter until the engine fires regularly and the engine speed rises. Then ease off the accelerator slowly. Cranking times of up to one minute will not do any harm to the starter.
At ambient temperatures of less than -20*C/-4*F, depress the accelerator three times prior to starting.
Idle Speed Adjustment:
Turn idle speed adjuster clockwise until the engine will just run smoothly. The idle speed adjuster should be turned clockwise to the stop (normal position) at latest when the coolant has reached a temperature of +60*C/+140*F.
I hope that helps someone.