I bought a 1999 RX300 AWD used recently with 195xxx miles on it and had no issues until recently at 205xxx miles. The transmission had been operating flawlessly until suddenly driving home one evening, I had just stopped at a stop sign and then continued on for about 1 mile until suddenly the tranny started to slip and eventually it was just totally not going in any gear, it was like I had it in neutral and was revving the engine pointlessly. I pulled over, put it in park, and went out and checked the fluid level, which was full, but the fluid was a dark brown, but full nonetheless. So I shut the engine off to contemplate my options. After sitting for 5 minutes, I decided to start it back up and see. To my surprise it went into drive and I started on my way again, to only have the same problem occur again. So I repeated this numerous times till I finally limped it all the way home, never clearing 40 mph before the problem required me to pull over. So I did some research, and yes, I was dismayed to learn about the tranny problems this vehicle has since its introduction. But I found someone who had the same symptoms and learned that he simply dropped the pan and replaced the filter/screen, refilled the trans, and it solved his problems. I did the same thing and it put my RX300 back in action and shifting better than ever. But now here I am a week later having the same exact issue again. And here's the question: Should I try flushing the entire transmission system, and then replace the filter again? The fluid does still have a burnt smell and a brownish discoloration to it again. Would I be wasting my time and money? Or should I be looking into finding a replacement transmission? And I've also read something about a bad ground issue as well, but I haven't had any DTC's to cause a check engine light to illuminate. Please advise, cause my wife loves this car and I want to get it back on the road for her.

 

Check my story, my cars runs well so far.
https://www.clublexus.com/forums/rx-...orary-fix.html

If you do not want to rebuild your transmission
My suggestions are :
1) First do a few drain and refill transmission fluid again and let the engine run. You have at least 50% old fluid was not been changed.
2) Do change the transmission fluid and filter again
3) Put a bottle of Lucas transmission fix in your transmission fluid

Last but not the least,
Make sure your transmission fluid level is correct, my transmission shift quite fine at low fluid level (short about 0.6 little) but I refill it to normal level anyway. Although I get a bit worse accelaration and MPG but seems a bit more reliable.
Good luck

Quit a few professional people told me not to flush transmission if transmission fluid has burned smell and brownish discoloration. Your transmission may fail immediately......

 

If you want to change your fluid again I would recommend using Max life it can be bought at Walmart around $20 a gallon it's a fully synthetic transmission fluid. I bought an RX 300 last October 2015 the planetary gears are making noise I change the filter and did a drop and refill of a total of 16 quarts. The transmission is holding up so far for about a year and 16,000 miles I do a drop and fill just about 4 quarts I driving about 20 miles to another drop and fill to let completed 16 quarts $80 worth transmission fluid. I don't know if this will work for you this will give your transmission about 90% clean oil and synthetic oil does work a little bit better in the transmissions. You can also use it you power steering I changed my transmission and power steering every 30,000 miles using Max life. I use mobile one extended service in my engines I have driven Toyotas over 500,000 miles and nothing is ever wore out using synthetic oil.