rpomerle

I own a 2000 Lexus RX300 with 338,000 miles. My MPG have been slow but steadily decreasing. Used to get 21-22 now down to 16.5. Car runs amazing, almost like day 1, although I have been through the usual 2 transmissions. Any ideas on what might be causing the decline?

ToyotaLexus

wow... that's a lot of mile.... how much does it cost to replace the
transmission?

as for the MPG... I used to get at least 22mpg, at 70mph in cruise control.
Now it's dropped to just 20mpg.... not sure if it's the cold weather...

rpomerle

New trans. range from 4000-4800. Used vs refurb.

thomas1

I am impressed you have the highest mileage that I have read about. Have the Air/fuel sensors been changed in a long time....(look like oxygen sensors on the front and rear of the engine)

rpomerle

CEL has been on and off for a month now...was able to get to my lexus mechanic with the light on and found it is an air/fuel sensor. 90% of the time the CEL is off. So perhaps I should get the sensor replaced. I have owned the car since it had 40K miles...I have never replaced the spark plugs? It runs as good as a car with 10K miles...so I was hesitant to really mess with much.

lexus114

Holy........!!!! you never changed your spark plugs?? Well my friend,I would start with that,and change your a/f sensors,(because if you only do one,the other will fail with that millage on them)Check your timing belt too.BTW,what oil are you using? and fuel? This could be very good information for the board.

edbro

I would too but, on the other hand, it is hard to argue with success!

Lexmex

rpomerle,

Do you remember the actual A/F sensor code you got?

rpomerle

I do not know the actual code for the A/F sensor failure. As far as oil...just regular Mobil every 5k. Fuel always 87 octane and no one particular brand...when I need gas I get it where ever. Some other Lexus owners I know swear that Citgo gas gives them a boost in MPG. I haven't got the time or patience to always track down a Citgo station! As far as timing belt it is due to be changed.

lexus114

Thank you for sharing this information with us.But start with fixing the bad sensor,and plugs.You may want to check you air filter too.

absorbing

After I replace the knock sensors my mpg has 30% better than before, even though I change a/f ratio sensors, new air filter not improve obvious,new spark plugs only give mor power feeling , so make sure change knock sensor because it affect you ignition timing if go bad!