i garantee it will be the coil packs. it will be hard to find which one it is, but it will start getting worse and worse. what you can do is pull the cover off, let the car run until it starts to miss fire. then disconnect the coil packs one by one. with each one you disconnect the idle should get even rougher, until you disconnect one and the idle doesnt change. then you have found your faulty coil pack.
same thing has hapend to me with both my skylines. with my old gts-t i just replaced them one at a time as they went. but with my gtr i lashed out and got a set of splitfires.
i can highly recomend the splitfires. ive never had a problem with them.
hope this has been a help.