Before I started driving for mileage I think I got two tanks at the EPA highway rating. Ever.

And those were overnight treks through CND, where I didn't want to get stopped by a French speaking cop or pay their gas prices so filled up before crossing and kept it slow. 25 mpg was just enough to get me back into the US to fill up again.

 

In theory, a wide-open throttle is more efficient than a partially open throttle.


Isn't that one reason why un-throttled diesels get great fuel mileage?

 

My wife drives a 2009 Sport. Current mileage is 131,500. No major problems. Routine maintenance includes lots of oil changes, trans fluid, air filters and front brake pads. This car gets 30-34 mpg all the time. (Mixed highway commute and surface roads.) On a trip it will do better than 35 mpg at continuous speeds of around 65 mph and around 30/31 mpg driving at 80mph. As stated above: (1) Ditch the computer and calculate your mileage by hand. My computer always reads 3-5 mpg too high. (2) Check your tire size and inflation. The wrong tires can throw off your speedometer, odometer and computer. Manual calculations will be wrong if the tire circumference is significantly different from OEM.

 

Another thought. I just noticed that you live in California. When I lived in Colorado, they would "reformulate" their gas every winter and my mileage would drop 2-3 mpg until they changed back to summer gas. When I lived in California, my 92 Civic came with California emissions equipment which was different than the rest of the country. To be fair, you should compare your mpg to California vehicles since the gas and emissions equipment may not be the same as the rest of the country.

 

Our '13 A/T gets about 24 mpg with just short trips in traffic, about 30 mpg on longer suburban commutes with occasional freeway, and better than 40 MPG in flat freeway driving, ~65 mph. In your case, I would use an OBDII scanner to pull codes - the O2 sensor is far from the only item in the loop. If nothing reads amiss, have the exhaust checked for excess HC and look at the color of the plugs.

Steve