Its hard to say really, it sort of sounds like its misfiring but its not if you know what i mean, basically when it boosts up it will hit about 4000rpm then it will hold back but not cut out. every other turbo car ive owned cuts out quite sharp,like the rev limiter on my rs but this doesnt cut out it just burbles and will sit at about 4000rpm,if you lift off a bit and are gentle with the throttle it will rev right out but like i said it only does it in 2nd gear or when you drop down a gear sometimes.