I have a 2001 Corolla S with 72K miles. Fuel economy is very poor averaging 240 miles per tank. It is mostly city driving. Even when on longer trips, it went to max of 30 mpg on Chevron premium gas. Used Chevron Techron on a tank of gas hoping to help fuel injectors when I used ordinary (87) fuel couple of months before. Cleaned Mass Air Flow (MAF) sensor. These did not help yet after 2/3 tanks of gas. Changed spark plug (NGK Iridium - no gapping check done), transmission oil, thermostat, condenser and engine coolant around 4 months before. Condenser was changed because of bird hit. Rest were done as maintenance by an individual mechanic. On current gas tank, I may get 240 miles on Chevron premium gas (without extra Techron) for city driving. There is no Check Engine Light (CEL). What else could I check? Read on internet about O2 sensors, fuel filter, etc. Am not very handy with the car, so will need to locate another Craiglist mechanic. Going to shop or fixing it with dealer might be too expensive for this cars market value. Don't want to throw new parts hoping it will fix, while issue could be unrelated. Tires are at 36 to 38 PSI (recommended is 32).