2012 ISX 12 CM2250 - rough under throttle

[schISM]

Is there any CEL’s for high NOX or PM after the hazy smoke episodes? What you’ve described regarding SCR warm-up mode is normal for this engine. It will run in this mode until it’s reached operating temps and the DOC is converting hydrocarbons into CO2 and H2O. Now this is purely speculation on my part, take it with a grain of salt. If the EGR cooler failed and contaminated the DOC no amount of cleaning will bring it back...it’s dead. The ECM wants that DOC to light off so it closes the turbo forcing more O2 through the engine and raw fuel into that oxygen rich exhaust stream via a post injection pulse trying to get that catalyst to light. Now that in and unto itself won’t cause a healthy engine to stumble and perhaps this is where your engines mileage may come into play. If the ECM is commanding more and more fuel to light the DOC that isn’t going to light on an engine with 790k that more than likely is getting a bit low on compression perhaps it would cause it to stumble. Again I’m just thinking out loud, as it sounds like you’ve covered your bases. Good luck and let us know when you get it figured out