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2000 Rx300 Loss Of Gas Mileage

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Can anyone help with a sudden loss of gas mileage in a 2000 RX300 AWD. It dropped from just below 19 MPG to 16 MPG almost over night. Have cleaned the mass airflow sensor and changed the thermostat - was heating up slowly. Any other ideas?? No trouble codes. Runs well.

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checked the usual, tire pressure, air filter, and dont forget the change in fuel from winter to summer blends....With no cel lights hard to diagnose

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Just had the CEL come on this morning on the way to work. Code 1150. I believe this is the Air/Fuel ratio sensor on the front bank of cylinders. Bet that could make a difference in mileage. Thanks for the input have checked all the other typical culprits. Was about to remove wheels and check for dragging brakes.

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