Truck Repair: rough idle, ford f800, head gasket

Question
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Followup To
Question -
what would couse a rough idle?we just replaced head gasket had head tested and pressure checked,and still have rough idle,we thought maybe it was an injecor and replaced it but still have the same problem the truck is a 99 ford f800  with a cummins motor.do you have any idea's. also had new springs installed on the head.thank you for your time and input.
Answer -
What size Engine? 5.9

Answer
Should idle around 750-800 RPMs.Is it seem like it is on one cyl or several?You can check on a misfire by breaking the fuel line loose one at a time at the inj or pump.Valves should have been set on 0.010 for intake & 0.020 for exhaust.In some cases the pump could be the problem of not supplying the correct amount of fuel for a cylinder.