BabkenBMW

I drive a 1997 BMW 523i with steptronic transmission and have a problem that annoys me. When I drive at a speed of around 40km/h and want to accelerate a bit, the car doesn't respond at all. I have to press the acceleration pedal to the end, and just then the car accelerates but as you understand the acceleration isn't smooth and makes the passengers feel a bit uncomfortable. As far as I know BMWs suffer from such kind of a lag. But if it was so, nobody would buy BMW. So I think there is a problem with my car.
Can anybody help me on this issue?
Thanks