06 cat acert

Have you had any check engine lights, or any codes in the ECM ?

 

Sounds like a unresponsive Iva but it will usually log a code,
when the truck starts the ECM controls a sequence for the Iva system, coolant temp is a big factor on the sequence, and opens and closes the control valve for the oil supply to the Iva system.
low eng oil pressure can cause your problem, aerated engine oil, vva bleed holes plugged, vva adjustment out, faulty Iva pressure solenoid.

Could be one of many things causing the problem your having.
if you have et you can do some tests .​

 

Seems to be a common issue " acert runs rough when cold "

Mine will do it also sometimes. It hasn't yet this year so I'm keeping my fingers crossed, but I'd love to know exactly what the cause is.

If you figure it out please post your solution.

 

I'm confused, does it run rough til the water and oil temp comes up( thats normal for mine) but if it stays rough after it reaches operating temp somethings wrong

 

Mine did that too untill I had it inframed. The head gasket must have been blown I drove it that way for years. Then it broke a compression ring and had it inframed. The headgasket was blown between cylinders and it had been run so long that way I had to replace the spacer plate.
Cat said that the head gasket would cause a cold mis. It runs/pulls smooth cold or warm now.

 

It's not the same thing as when it runs rough until the engine is up to temp. I've experienced that in the past also. That one is much more severe of a poor running condition.

Instead it just seems to run a little off, most noticeably under a hard pull when lugged down a bit , all day long. This is just in the winter on cold days with winter diesel. It just seems to shudder a bit.
When the weather warms up it's silky smooth.

It's done this before and after my inframe.

Sorry if I'm onto something other that what bob1234 is after but I think we're dealing with the same symptom. Very frustrating, and like I said I haven't had it yet this year. If it returns my next bright idea will be to try a winter front and just do what I can to keep my temps as high as possible.

 

I have 06 625 mxs, truck acted the same as you described, I was thinking IVA's, no codes for couple months. Then got code (I think 26 but my memory sucks). Replaced barometric pressure sensor and no more issues. Look forward to hearing what solves your issue.