Rough Idle:
Not an unusual problem with our cars.Not all 350Z's have it but a good number do.mine was fixed via a new MAF and a grounding kit.
Other causes have been found too, but most commonly it seems ot be grounds,... about 5 out of 7 PPL with this problem were able to fix it with a grounding kit but not all.
In some cases coil packs or MAFS were found at fault, in one rare incidence the injectors were leaking air at a gasket ( this one is pure hearsay and only one I heard with an injector replated problem).
Depending on the quality of your dealership , they will fix it under warranty no questions asked (albeit they will likely need it for a full day as its not easy to chase these idles down) or they may refuse to worry about it at all if it thorws no codes.
Check this thread for a story on this:
zerothread?id=105020
Fred..