ISX flutters at idle

My 2009 ISX CM871 has fluttered at idle since I bought it a year ago. It does this no matter which of several tunes is in it. It also builds boost slowly up to max, then drops 7 or 8 pounds and holds there. Also - it gets really decent fuel mileage when loaded up to 60,000 - 65000 gross above that fuel mileage plummets. Any ideas what's going on here?

 

Just a guess I would say the turbo is sticking or not going full range of movement

 

My 08 would surge, if that's what you mean. It was the EGR sticking. Pete replaced that one. Talked to a Cummins engineer at Louisville[MATS] and he suggested removing the EGR and cleaning it on a regular basis. I did that and had no more trouble. Very simple job and easy!

 

Yes, surging is a better description. However my egr is in "test mode" and should not effect anything.

 

If you have perchance removed The EGR for off road operations, I see what you are saying. If it is still on the truck, I would pull it off and see if it is maybe it is not opening all the way. First time I had about an hour in R&R plus clean up time. It's basically a lawn mower valve with 2 tulips. The spring is pretty weak, I just pushed on it to get the keepers off.

 

A slight amount of air in the fuel will also cause this. Could be sucking in a small bit of air from somewhere.

 

http://www.thetruckersreport.com/tr...3-cummins-isx-cm871-technical-discussion.html

 

I had a surge/fluctuation at cold and then with time hot idle for some time with the truck I sold (in my signature). After chasing this for several years and swapping everything left and right. Including fuel actuators, shutoff solenoid, both fuel pumps and several sensors, I've finally nailed it with swapping "exhaust pressure temperature" sensor. Located on the "hot side" above the turbo towards the front of the block. Though mine was the 05, EGR only (with the "block").

 

I replaced that sensor a few months ago with no change. Along with nearly every sensor on the thing. Right now have it in shop checking actuator, turbo and for air on fuel.

 

Is your turbo actuator is still air controlled or electric? See if they can do a fuelling/timing actuators adjustment. Cummins did that for me once, it helped a bit. But didn't completely removed the idle fluctuations.