If the miss is present at idle do the Injector Cutout test and locate which Cylinder the miss is on.
(Injector Cutout Test: While the Engine is ideling loosen one of the of the Fuel Injection Hard Line Nut at the Injector or the Fuel Injection Pump; that cuts off the Fuel that would be injected into the Cylinder. If the Injector is good your miss will get worse and the rpm will drop. If the Injector is bad there will be little or no change in the rpm.)

If you did the above you actually located the Bad Cylinder. To see if it is the Injector you need to swap the positions of a good Injector with a the suspected Bad Injector.

If the Problem follows the suspected Bad Injector you have an Injector Problem. If the Problem stays on the same Cylinder you have a problem in the Engine or inside of the Fuel Injection Pump Element.

If you do find it is the Injector you also have the option of replacing one Injector or having that Injector tested to see if it can be reused.

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84 300D, 82 Volvo 244Gl Diesel