Surging at idle

[Ram4x4]

Recently my 5035 has gotten where it will surge when idling. When I go to full idle it kind of remind me like someone very slightly giving it some gas and letting off, giving it gas and letting off. It doesn't rev high or anything, just slight constant surge.

Once I get the RPM off idle, it runs perfectly smooth, no sputtering, no surging, just does it at idle.

Is this a timing thing, or?

 

[JerryK]

Small air leak on the tank side of the fuel pump [ loose connection, cracked hose, etc. ] will suck air and do it..... amongst other things.... Some older Dodge Cummins owners had to replace the soft lines going from the frame to the motor mounted lift pump, or just relocate the pump to the frame and put in a 'big line' kit to fix the problem. If a leak is the problem, when it gets bad enough it will allow the lift pump to loose prime and you will have a hard time starting it.... if that's what it is.

 

[JerryK]

Here is a list of other stuff.... add to it, poor fuel, etc.

Engine speed surges at low or high idle

1 Fuel level low
Check/fill the tank.

2 The condition occurs at idle, the idle speed is set too low for accessories
Adjust the idle.

3 Throttle linkage mis-adjusted or damaged
Adjust or repair the linkage.

4 High Pressure fuel leak
Inspect the high pressure lines, fittings, or delivery valve seals for leaks and repair if necessary.

5 Air in the fuel system
Bleed the fuel system and check for suction leaks and check for malfunctioning supply pump.

6 Injectors worn or malfunctioning
Check the injectors and replace any malfunctioning injectors.

7 Fuel injection pump malfunctioning/delivery valves malfunctioning
Remove the fuel injection pump and repair or replace as necessary.