Check the Glow Plugs first.

If an Injector is not atomizing well it will show up when the Engine is cold and appear to get better when the Engine is Hot. Simply because when the Engine is Cold poorly atomized Fuel is harder to turn into a vapor and ignite when the least amount of heat is available in the Cylinder. When the Engine reaches operating temp it is easier for poorly atomized Fuel to turn to a Vapor and ignite so the problem would decrease.

And, then there is the Ball Pin inside if the Prechamber that the Injector sprays Fuel at. Once that is nice and hot it must be a big aid to poorly atomizing Injectors.

Also a worn out Injector is more likely to show up at idle because the Fuel has more time to dribble out of it. A worn Injector Nozzle will atomize better at high rpms that at low one as a larger volume of Fuel gets injected out in a shorter period of time.

To check for a bad Injector check in the DIY section for the Injector Cut Out Test or do a Google search.

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84 300D, 82 Volvo 244Gl Diesel