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Bad O2 Sensor? - Gas Mileage Plummets!


ScottRX300

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I have a 2002 RX 300. Since I've owned it, I've gotten 20 mpg (+/-). Recently, the gas mileage suddenly plummeted to about 16 mpg. It wasn't a gradual drop-off -- one tankful I got 20 mpg, and the next 16 mpg.

I'm thinking I've got a bad O2 sensor. Does anyone have any thoughts on this?

Thanks for your help.

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Exact same type of driving? Same conditions? Same gas station? There are so many variables and 4 mpg isn't that crazy of a change. Is it possible you didn't fill up your tank all the way last time? I did that once.

The only reason my RX300 has dropped from 19-20mpg to 13-14-15mpg was our nasty winter season. For some reason the '99 engine (at least) reacts horribly to cold weather. However, your profile shows lovely Southern California...so that must not be it. Say, any Linux sys admin job openings out there for me to get me outta the cold? ;)

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If you have a bad O2 sensor or any sort of engine problem, your check engine light will come on. I have two RX300s and they both average around 20mi. per gallon according to the meter inside the car. They used to get around 18mi. until I started using Mobil 1 synthetic oil, and a K@N oil filter and air filter. There is also a noticeable difference in the performance of the car and the synthetic oil works great in cold weather. I use the high octane gas, but sometimes my wife uses the lower octane which causes the gas mileage to drop slightly and the car to run sluggish. It's a good idea to add a high grade fuel system cleaner to your tank every 5k for better engine performance.

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I know here we do have to deal with reformulated gasonline and ethanol added gasoline -- both of which can cause a tad lower mpg, but 4 mpg? I doubt it. However, if you see a strange man driving WAY out of his way to put 100% unleaded in his tank, you'll know it's me.

I've also noticed the RX mileage really reacts to the driving style. If you like to coast and keep the RPM steady, I think you can squeeze another 2 mpg. If you like taking off from stoplights and lots of acceleration, you'll probably lose 2 mpg.

That's some good info blustu...I think I'll try some of those when the weather turns cold. And ScottRX300 thanks for your thoughts, my wife and are actually planning to relocate to warmer weather climates soon. My RX is originally from Sherman Oaks, CA and I'm sure it would love go home!

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You didn't just put new tires on did you? Sometimes new tires of a different brand have a different rolling resistance and can cause a drop or rise in MPG.

Jeff

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