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Gas mileage on 1999 Toyota Corolla

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
My gas mileage drop I already change the fuel pump, coils and cleaned the Oxygen sensors but I still get low gas mileage on my car
(1) Answer
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There is no real way to clean the Air fuel ratio/O2 sensor the sensor is key to fuel efficiency but the pattern has to be monitored on an oscilloscope to determine if it is OK or not. Your car has On Board Diagnosis 2 (OBD2) using a scan tool it would be interesting to see what the Long Term and Short Term Fuel Trim figures are , a scan tool can show if the computer is adding or subtracting fuel. The air flow meter and coolant temperature sensor are two other key inputs contributing to good fuel economy.
Here is a US government link to Corolla MPG.
http://www.fueleconomy.gov/feg/noframes/15040.shtml