Rough running when cold, slight surging under load.

Greetings from downunder.

My 2010 vrs 2.0 is running rough when cold.  So far I've had all injectors & plugs changed and a remap.  No code shows.

Its' particularly rough about 1250-1400rpm.  Driving it when cold is jerky, particularly at those rpms, so much so my wife won't drive it until it's warm.  It's mostly ok when warm, however, I've noticed that it's surging on cruise control on inclines (under load).

VCDS shows misfires in cylinders 2 & 4.

Dealer has "checked" coil packs and fuel flow.

The car has done 156k, 99% of which is on cruise control on the highway.   I'm leaning towards carbon build up in the inlet ports, especially as the last time it was returned to me they noted it (However, they checked it warm, so told me it was fixed!!).

Apart from carbon build up, then only things I'm guessing it could be (and I stress I'm not a mechanic) are coil packs, fuel or air filter, however, high revs, warm performance seems ok to me.

Dealer currently investigating warranty clean of inlet valves.  It's the highest klm vehicle they get so everything seems unknown to them, but it will help them in the long run when other customers start exhibiting same symptoms.

Am I on the right track?  Any other suggestions?