Truck Repair: 2000 8.3l cummins bad idle, freightliner fl70, coolant temp

Question

---no codes   no smoke  sounds like a gas v8 eith bad plugs/wires on a cpl o cyl    onl at idel tho...what about putting another supply pump inline?   thanks----------------------

Followup To

Question -
i have a freightliner fl70 with an electronic 8.3..it runs  good  good fuel mlg  etc  but   it idles iratic....when u first start it its ok...after u run it then it starts...now!! any load on the negine makes it idle ok  ..such as -- air compressor, air condition compressor cycle...turn the ac off and the bad idle starts,,,,,and fast idel helps but not all the time,and not 100%...fuel supply pump working,new filters, new tps..sometimes its really bad...ive been living with it but   i shoulnt have too    help   thanks re

Answer -
No fault codes?The electric transfer pump is for priming only.It runs for 30 secs the shuts off until you cycle the key for 30 secs.The CAPS injection pump has a gear pump in it.Sounds like a sensor reading out of range but not logging a fault for it because it has a valid reading but not an accurate one.Like boost pressure or coolant temp.Does it smoke any while doing this?

Answer
The primer pump just runs for 30 secs when key is turned on & then cuts off because it is a primer pump.The injection pump has a gear pump that supplies around 175 PSI in the pump.If it runs fine other than idle,then probably a sensor reading wrong causing the computor to adjust to the input from the sensor.