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Poor gas mileage

(2000 Acura TL)
in Springboro, OH on January 09, 2010
Had this vehicle since new...gas mileage degraded from 24-26 mpg to 18-20 mpg (20%!!!)over last year. The 24-26 mpg has been the gold standard for 8+ years on this vehicle (for me). Recently took a trip and hwy mileage was best ever: 28-30 mpg! Now back to commuting to work and returned to 18-20 mpg. No change to fuel used, EGR replaced, fuel system cleaned/decarbed, new O2 sensor, tire inflation good, etc, with no change. Motor mounts were replaced about 8 months ago and this fixed it for about 2 months-then back to lower mpg. HELP!
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Popular Answer
My Acura TL gets 24 to 26 miles per gallon if I drive at 60 to 65 mph. My first guess was an O2 sensor that was getting lazy. Your car has On Board Diagnostic capabilities a professional grade scan tool connected to ( common to all 1996 onward vehicles) a 16 pin diagnostic socket under the dash of the car can be used to look at O2 sensor patterns, and long and short term fuel trims for each bank of your engine, these figures will be key to figuring out increased fuel consumption. Air flow meter monitors air flow into the engine, if this sensor gets dirty fuel consumption increases and power drops. Fuel injectors over time may get deposit build up in the nozzles or the valve seat in the injector may deteriorate causing a fuel spray pattern that does not atomize as well as they did when the engine was new. Engine mechanical integrity and "state of tune" condition of spark plugs, air filter, fuel filter [where applicable], intake and exhaust valve clearances {where applicable], fuel pressure and pressure regulation also play a key part in fuel consumption.
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