The government mandated switch to 10% methanol also contributes to a decrease in gas mileage, although only about 5%. It's probably time for a tune-up that includes new plugs, fuel filter, and air filter. Also, look at your driving habits, they may have changed over the years. Avoid jack rabbit starts, anticipate stops, drive at a steady speed and accelerate smoothly, never at full throttle. Other than that, there is really not much you can do.

Change the filter, your spark plugs, battery and all your fluids. Yeah, it's honestly not going to be the same anymore because cars ware pretty easily, especially when it comes to gas mileage. Just keep being diligent about your car maintenance. Otherwise, you're doing all you can.

Also, freeway commute a lot more rather than the city. That will definitely save you $.

YEP tire TYPES is very very important! There are FUEL EFFICIENT tires that save gas. ALso it depends upon OUTSIDE TEMP and your choice of OIL types! using MOBIL ONE synthetic 0W_30 is a SURE WINNER as it reduces friction and SAVES ON GAS! Do NOT use VALVOLINE, the sludge maker ever! I have DE-SLUDGE many TOYOTA engines! PENNZOIL ULTRA gives a 15 year 500k mile OIL WARRANTY! It is about the CLEANEST oil you can use with HIGHEST test scores, and the official oil of Ferrari as well! <
How many miles are on it now?

A good tune-up including air and fuel filters is part of regular maintenance and would probably help the gas mileage.

Making sure your alignment is set correctly, transmission is serviced, brakes are adjusted correctly (where applicable) are also normal maintenance items that could effect mileage.

Finally, don't expect it to ever be as good as it was when it only had 7K miles on it. Engines wear over time and lose some efficiency. Transmissions also lose efficiency and can effect mileage.

You should be able to get it back up CLOSER to where it was back then, though. Losing 100 miles a tank is quite a bit.

Do you still drive the same route you did back then? Same amount of city VS highway driving?

I own a 2005 Toyota Corrolla in excellent running condition. When I first got the car certified used at 7K miles the gas mileage was fantastic, especially during the summer; I was getting over 400 miles to the tankful. Now I typically get a little over 300, basically about 100 miles less than I used to all those years ago.

The car still runs just as smooth; I've changed the oil regularly but have never changed the plugs or wires, nor the fuel filter. My tires are at normal factory suggested pressure, and there is hardly anything in the car to weigh it down except me and a few trinkets, but nothing heavy at all. I drive very conservatively and only used regular unleaded gas. Any suggestions? thanks!