I have read some problems that resemble mine but with some slight differences. My 2000 rx300 with 128,000 miles started to get a cel about a year ago and could not get a code. Finally one day it got a code for 2 knock sensors but everything ran fine with no problems. Now when we go on a long trip, over 45 miles it runs at 4,000 RPM at 70 mph. Note this does not happen all the time. So I pullover shut down engine and turn off key for 30 seconds or so and it shifts into 4th with no problem until I come to a small town where I have to stop or slow way down. Also note not every town just a few on a 400 mile trip for example. I have changed out tranny filter with no improvement and started thinking it has to be a computer problem or sensor. I have yet to try the disconnect battery cables yet. I'll try that when I get home. Any suggestions? Knock sensor? Also new symptom occurred the other day and has only happened once. It shifted through 1st 2nd and 3rd fine and before it could go into 4th the engine lost horsepower. You coud floor it and no response. But after pulling over and turning off engine for 30 seconds everything was fine.
