OK, since I have a MPG gauge on my 2008 328i, I do tend to look at it. I noticed something weird especially when you first start to drive off. So it starts at 12MPG and I coast to a traffic light that is about 2 minutes away. When I take my foot off the gas pedal, the needle moves left to the 50MPG range but as soon as I step on the brakes, the needle swings right to the 20MPG and then quickly back to the left to the 50MPG range when the car comes to a complete stop. BMW advises against "warming up" the engine, suggests driving off at moderate speed for the first few minutes. This only happens everytime when I first drive off (cold engine). Since I don't have a oil temp gauge, I don't know if its because the engine is still cold after 2 mins at speed no greater than 30mph. It doesn't happen the next time I have to come to a complete stop which is after driving 6 miles on the highway. Anyone has noticed the same thing or know why this happens?