cm2250 rough idle

[JimT]

Did it again this morning. Shut down for about 12 hours last night, started up cold, about 35F just outside of St. Louis. Ran ok for a minute or 2 then SCR warmup kicked in for a couple minutes. AFTER that finished it went back to normal idle briefly before it started lugging? surging? Not sure what to call it. It drops down to about 690-700 rpm for about 1-2 seconds then back up to 725 for 1-2 seconds then repeats. It only does this when the engine is cold and I first start it up, but not every time. Once the coolant temp started climbing above 100 or so it went away.

I don't know what could be going on. This is after I taped up the wiring harness and replaced the main crank speed sensor.

While I had the tools out I also went and cleaned up the DPF doser injector. As I thought, 4000 miles and it was already getting clogged up. Not a lot of soot packed in there, but enough buildup to screw with the fuel spray.