Concerning the Injectors it is really a matter of every little bit helps. To make starting easier you would like everthing on your engine to be working the best it can including the Injectors.
Unfortunately the only way to know for sure is the pull the and have them tested or have them rebuilt and unless you can do it yourself it will cost some.

If your Glow Plugs and Starter system are in order the thing to do that cost nothing is to re-adjust your valves. Some Members have reported doing so to be a big improvement in starting and power.
Next as previously stated at a slight cost changing to synthetic Oil; allowing the Engine to turnover easier when it is cold.

After that Camshaft and Fuel Injection Pump timing.

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84 300D, 82 Volvo 244Gl Diesel