Hello Everyone;
i have a 99 rx300 i bought used.
when i purchased the SUV, it wouldn't shift into O/D, Fuel Economy was TERRIBLE!! (Like maybe getting 14mpg on average at a great operating status)
I took it to the shop, and they told me the ECU Failed and All the O2 Sensors with it- so they replaced all of it, cost about $1200
worked alright overall.
then two weeks later, i noticed it was driving a bit odd, i thought since i bought it with 170k miles maybe its due for spark plugs as i had no clue what the previous owners did in regards to maintenance. so i put the first 3 in the front (turns out they were replaced once but the replacements werent iridium
drove a little better for a couple weeks and then it was like bloody hell, couldnt drive the car more than 20 mph, wouldn't go above 55, so i carefully drove it to the shop and left it for the people to see....turns out the 3 plugs and coils in the back failed so they replaced them...all went way better
So i got the car driving much smoother, shifting accordingly etc, fuel economy still had issues (using premium gas)
so i finally went and did a seafoam spray job on the intake and cleared so much junk out it was unreal!!!
Car drove AMAZING!!!
Fuel economy picked up (highway still wasnt right but was better than itd ever been prior!)
now its having intermittent issues with O/D again, codes read for one 02 sensor (will have to re-read codes and post in a reply here once i re-read)
What bothers me though, is i went to the lexus owners online site where you can type the VIN number and get all service history on the car, and noticed back in 2000, or 01-the ECU was replaced and all the 02 sensors!
Now im sitting here wanting to know WHY they've failed multiple times and what i can do to repair this! Because truthfully, this is ridiculous!!!
any ideas?
Is this something that regardelss of how long ago the original fix took place, i can do anything to get lexus to cover my costs if its an electrical short?
Any input would be SO APPRECIATED!!!
Thanks again!

 

I can't help with much, but the RX300 has three O2 sensors, two under the hood and one along the exhaust, just before the cat. Maybe your shop missed that one along the exhaust or it wasn't showing a fault at the time, so they ignored it. If so, maybe that is the problem.