Ok, then it's not the typical cause. On to the next possibility. If it's struggling only when the air is cold, there might be some dirt in the MAFS. This is a credit-card-sized sensor located in the air tube just in the back of the air pipe a few cm from the air filter box. Remove the screws and carefully slide the sensor out. Don't treat it roughly, it's a $400 donation to Nissan if you break it. Don't stick anything inside it, even if you notice black soot in there.
The way to clean it (have done this myself, and I think I've even posted a thread about it somewhere here) is to remove it completely and spray electrical contact cleaner in the small hole in the side, then let it drain out. First spray should come out black, maybe the second too - give it a few spritzes then hold it while the cleaner evaporates. Reinstall and see how it goes.
You can get electrical contact cleaner from Jaycar, but in auto shops it's also sold as "MAFS Cleaner" and is essentially the same thing.
Just remember, it's absolutely vital that nothing solid (toothpick, brush, Pikster etc) enters the sensor hole. Only the spray.