I have a 2008 ES 350 and it is in really perfect shape. Just this week, however, the gas mileage on the dash really dropped. I do the same kind of driving..mostly city and it's been consistently 22 MPG. All of a sudden it's around 19.8. What would cause this? It's confusing...

 

1st: don;t trust the onboard computer's MPG gauge. Only trust manual calculation. Miles / gallons.
2nd: When you've filled the tank up 3 times in a row, figured out the gas mileage manually, and then notice a significant drop, then you can question a possible problem.

Assuming your mileage went down, one tank's numbers could mean you simply got some crappy gas. This time of year, the gas blend/formula starts to get changed in certain parts of the country. There is a difference in the gasoline you get between summer and winter. You could have gotten a crappy tank full or maybe the blend has changed and your car's computer needs to readjust.

Again; don't worry about it unless you get significant'y worse mileage on a number of fillups in a row. And don't measure based on the onboard computer. Do it manually.