I've had my 2001 cab for about 2 months, 4000 miles and love the power, handling and finesse of this great car. I cannot find information about how the "Sport" mode works. Obviously, there is more power and more responsiveness from the gas pedal so I assume there is a change to the air/fuel mixture. I usually turn it on right away. Why is it even there? There is a gas guzzler tax anyhow on the M3, so fuel economy seems a secondary concern. The car is great either way, but it seems unnecessary to turn it off.

My understanding is that sport mode merely increases the throttle-body butterfly response rate. It does not actually extract more power from the engine.

For example, let's say that sport mode doubles throttle response (I don't know the exact amount of increase). With your foot half-way to the floor, in normal mode the throttle-body butterflies would be half open. Pressing the sport mode button would snap them to full open. But you could get the same effect in normal mode by slamming your foot to the floor.

Agree with above explanation.When I start up I immediately activate sports mode and never drive with it off.Doesn't seem to make a significant difference in gas mileage either.
But be careful activating it when driving since the car does bolt foward.

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