2012 D13 not holding Idle

Hello, Just wondering if anyone has had an issue where once you set an idle RPM once the truck goes into clean Idle mode the rpm's drop about 150 RPM even if i make a new rpm request within 20 min it drops again. it just started doing this before once I selected an RPM it would always stay there. My truck has about 300,000 miles on it now it's a 2012 VNL 780 with the I shift and D13. Ive already taken it to volvo about the issue and was told that it's notmal and once it goes into clean idle mode the truck does what it wants and they cant change any settings in the clean idle mode. I know the truck needs to keep pollution down under 30ppm and I havent cleaned the DPF yet, Perhaps is it possible that the truck is dropping the rpm's down to keep it under 30ppm? all I know is 800 rpm is the trucks sweet spot and thats where I leave it if I need to run all night. it drops down to 650 rpm which is a bit of a rougher idle that is really annoying, even if I '' Make a New speed Request" it doesnt take long before it drops again.

Any ideas would be greatly appreciated.

Ryan.

 

Just had spn 4752 pop up. Delta p sensor. I bet that would have something to do with clean idle.

 

agreed. mine idles up to 1500Rpm when I idle for a long time. thats normal like you said. that code I got was related to a plugged up EGR cooler, Volvo blew it out with compressed air I guess it was really dirty, noticed the truck idled better (smoother) but it still does not hold what ever idle I set it at.