I have a 2002 RX300 with about 60,000 miles on it. Since I've owned it, I've gotten +/- 20 mpg. Recently, from one fill-up to the next, the mileage plummeted to 16 mpg. There was no gradual drop-off...it just droped from 20 to 16.

I'm thinking I've got a bad O2 sensor. Anyone have any other ideas?

Thanks.

 

how do u know u have a bad 02 sensor???

 

A bad 02 sensor is a possibility, though not too probable on a vehicle as new as yours, especially if you're not seeing a Check Engine light. The ES/RX V6's occasionally suffer MPG drops from having a dirty throttle body intake, and both times my old ES suffered dramatic MPG drops, it was (get this) a jammed front brake caliper, once on the passenger's side, and a year later on the driver's side.

 

I thought I might have a dirty throttle body, or something else in the fuel system. I ran two bottles of Chevron Techron through the system, but no improvement.

 

Pull your negative battery cable for about 30 minutes (to get any juice out of the capacitors). Additionally, check your air filter and I would also spray some carburator cleaner into the air intake stream. Also see if your MAF sensor (Right after your airbox) has crud on it.

Techron is good stuff, but I also like Restore fuel injector cleaner and also the one made by NOS.

I recently started using this stuff, http://www.nology.com/powerboost.html

The nology product improved my HC count down to 34 from 104. Also gives a fat boost of power.

 

on a 4 hour trip last weekend, my 2005 RX330 was doing about 18MPG onthe first full tank. On the return trip, i did another full tank, and was doing 23MPG. go figure. The only change was the gas station. I was running the same speed. So, i guess, a big factor lies on the quality of gas from each station that you use. I use super.

 

lof will lower 104 ppm to 34 ppm

my honda ulev car was blowing 25ppm after lof 0 ppm hc's

 

american gas already have cleaning agents in the fuel. try going to premium shell. otherwide make the ecu brain dead. and see what u get. and btw do u have the ac on?

 

LexMex: Though I've never done any work on the RX300, I'm pretty experienced with cars. I've never heard of disconnecteding the battery for a problem like this. Can you explain the theory behind disconnecting the battery, and how it impacts my mileage problem?

Thanks!

 

Koolaidman:

1. I only use premium fuel...and have since day one.
2. When you say "make the ecu brain dead," what does that mean and how do I do it?
3. I always have the a/c in "auto" mode...even when I was getting 20 mpg.

Thanks!

 

In the U.S., it is easy to do that but very hard to lower HCs in Mexico City to 34 on an SUV when you are using even Premium gas with a sulfur content of 220 ppm. Even the guys at my shop where I check my emissions were impressed as most new SUVs cannot clock that down here.

We have some of the worst gas in the world here...any wonder why we have pollution problems. I knew there were problems with the gas when I moved here and the Pemex station attendant asked me if I wanted an additive. I told him I am filling up with Premium...he told me...it's your car.

Gas may now be cheaper in Mexico but its quality is pure ....

When Koolaidman says make the ECU go brain dead...disconnecting the battery does exactly that. It resets the system. Before I head up to my track, I disconnect the negative portion of the battery. Then I run it up the toll highway up to the track...flooring it for 15 minutes. My difference in the 1/4 mile is .3 because of that.

This is known as adaptive transmission and your RX will manage air/fuel and a host of other parameters based on how you drive.

Even climate can affect it.

While this may not be the answer...it's worth a shot.

BTW, I now get like 13 mpg up here, but I have lead foot. More like 10 mpg on the way to the track.