Like I said once before, this car does not get the best mileage when you baby it. I tried so many technique, and so far I find that you have to mix both easy and semi-aggressive driving to get the best mileage. The best I have gotten is near 21mpg, and the worse is when I first got the car which resulted around 18mpg. Also, I do think that IS burns alot more gas when in idle, and that may explain why your mileage just drop like a rock after being through a 10 minute traffic jam.