I might be wrong on this, but i think the operation of the flaps work like this, put your foot down hard, like kicking down on an automatic, flap closes, more fuel delivered to the engine.... hey presto, more initial power. But i can also say, having driven my mates 3.0 litre tdi, mine seems perfectly ok.... even with one not operating... i would go as far as saying, the power difference is very small indeed if recordable,
My car still drives like a bat out of hell, no probs.... even pulls a family size touring caravan as if its not there, still the best car i have ever owned in 30 years.