Cummins ISX cold start rough idle

Monitor your coolant level closely. Newer ISX's are known for the EGR Coolers going out. They usually start leaking internally very slow and gradually get worse over like 3 months before final failure. They do not show up on any diagnostics. If it's not that, i would have some kind of gasket failure going on.

The fluctuation is the computer trying to correct the situation by varying the fuel.

 

sounds like its due for a overhead check, id have someone run the rack.

 

sounds like you have some fuel drain-back, surging issues on start up are generally due to air in the fuel, if your priming pump is working then try cycling it 2-3 times before starting and see if that helps? If priming pump is not working then once you start it after 30seconds or so rev engine up to full noise and back to idle several times to purge out any air in fuel system. If either of these seem to help then check for a leak around priming pump mount, debrie in a check vale and any signs of "wetness" on fuel hoses and fittings including around the priming pump.

 

Sorry to bring this thread back, but i have the same problem.. Did you ever fix this issue. Same engine cm870, rough start when cold, like sputtering after about 15 min it evens out.. i ran my overhead nust last year so that shouldnt be my problem and all fluids look normal w no signs of other contaminants to say it was from the egr cooler.. any input will be greatly appreciated!

 

As i recall it can be caused by fuel pump actuators. Also ive seen youtube video with guy taking out check valve . It looked nasty. You might want to check it too

 

How many miles on the truck?

 

Both my ISX trucks, one an 09 and one a 07 (cm871 and cm870, respectively) have always had a rough start gallop on cold mornings. Anything below 30 and they'll chug for a while. It's been just normal for mine. Addition of a block heater or running the apu on such nights fixes it.

If you're worried about an EGR cooler leak, pull open the exhaust recirculation pipes where they rejoin the intake side and look for the green/white telltale snot inside. It literally looks like boogers.