My diesel engine starts up normal. The problem is after the engine gets warmed up it starts missing at low rpm. Not as noticeable at higher rpm. Serviced at regular intervals. Has been parked for nineteen months, started at least once a month during that time. Any ideas as to what is causing the missing?

Have you purged all water and changed the fuel filter? I suspect fuel degradation. Try adding as much new diesel fuel as you can.