I have a new 2013 WRX with 550 miles on it. I've noticed it has a Lumpy idle when cold you can feel the car shaking. It's not a missing plug I don't think it revs fine and drives fine. Let it idle when warm and it'll miss every now and then. I had this on my SVT Lightning it was just he nature of the NGK plugs. I'm assuming its the same with the WRX. Just checking to see if this is normal. Only mods are a drop in K&N and Nameless Performance axle back muffler delete.