I have 82k miles on my RX330 AWD and my fuel mileage has dropped off about 10-20%. I used to get 24 hwy, now I'm lucky to see 20mpg. When I changed my oil, I located the A/F Ratio and O2 sensors. The A/F sensor on the firewall side is extremely difficult to reach the wire harness. Has anybody change them on their own? Do you need to drop the drive shaft or the exhaust Y pipe? Any DIY's out there?

I just replaced my tires w/ Bridgestone Alenza's from worn Michelins with no change in MPG. Everything else is still original. I know I'm due for some fluid changes too.

 

The 3MZFE engine in your RX330 is close in design to the previous RX300, so you might want to take a look at this, https://www.clublexus.com/forums/rx-...el-sensor.html (and I added a few pictures from my own experience).

I would caution that if you are not getting a check engine light, then I wouldn't play with the sensors yet. Usually after the 100K mark or more is when the one or more the A/F sensors (two upstream sensors) will throw a CEL and much later the O2 sensor near the cat (the O2 sensor is purely emissions related).

I don't know how long ago you replaced the tires, but we just replaced the tires on our 4Runner and noticed a drop in mileage (needed over a month), from 17.3 to 16.7 given of course because the tires are bigger when new.

 

I have about 1500 miles on the new tires. I'm not rushing to do the sensors today because it will take some time to recoup the cost of the 4 sensors. It was an idea if they weren't so expensive and there wasn't one in a difficult location. 3 of them are reachable, just the one looks as bad or worse than changing spark plugs.

 

Have you checked for error codes? Sure you have an issue with your O2 sensors?

 

I don't have any error codes. I've read that these sensors get lazy over time and should be replaced around 90k. If I wanted to replace them, it would be no problem except for the A/F Ration sensor on the firewall side. I couldn't even reach the harness connector from under the car. The exhaust system and the drive shaft was blocking my path. I was hoping to find someone that has done this themselves.