ur turbo is dependant on the exhaust gases reving it up, so ur gonna get boost if u just rev on the engine in neutral and there is enough exhaust going thru the turbo to wind it up enough, but you should not get near as much as if u had a full load during normal acceleration at the same higher rpm, how many lbs of boost are u normally pushing? and does it only push alot of boost when ur reving in neutral at high rpms?, do u have a really small turbo that kicks in at early rpms? you could just stop reving it up into high rpms when u dont want power, may be functioning normally.