Time to bite the bullet me thinks
Had this problem once for approx 2hrs....
changed spark plugs, put car back together ......
sounds like a WRX!
take coil packs / plugs etc etc out again... tighten!
SKYLINE again!
in my opinion it was just a loose connection or something I hadn't tightened properly. Obviously yours is something more serious but everything points to the coil packs so if you can be bothered buy 1 and swap it round till you find the right one........ or if your made of money just replace em all :wassup: