I have a 2005 RX330 with 91K; when should I replace the timing belt?

 

Yes, that would be advisable, not only due to millage but also since it wasn't done before, the age also comes into play, 12 years for a timing belt is a long time overdue.
Mostly likely cracked in several places by now, also since the labor would be the same, the Water Pump & related parts, Tensioner etc. should also be changed.
More info here:
https://www.clublexus.com/forums/rx-...z-s-rx330.html

 

As soon as you get done reading these posts! That's way too long for a timing belt, you are fortunate it hasn't already let go. Were this me, because of the time, I'd replace the tensioner, idler if it has one, and water pump.

 

I waited as long as possible to have the timing belt and water pump replaced because I had just purchased the car at 109K and wasn't able to spend the extra money on it at that time. Finally at 130K there was a persistent noise that was the water pump. I had both timing belt and water pump replaced and I am sorry I let it go so long. The car handled well in my opinion before the replacement, but I guess I didn't realize how the car SHOULD handle. The work improved the car's performance tremendously. Everything is smoother, the acceleration and deceleration are a dream now.
The mechanic showed me the removed parts. The water pump, tensioner etc were aged and the timing belt had some fraying. He said the belt wouldn't have lasted another week.

So my advice is to get it done. Your car will be happier and you will be a happier driver.

 

Just bought mine a week ago with 145000 on it. No sticker saying the timing belt was ever done. It runs very nice. Wish I could look at it and see if it was ever done,

Looking at the Aisin kit with the water pump just to be on the safe side. I hear its not good to break a belt on these. I am 57 and this is my first Toyota / Lexus.

 

Did you check the link posted above?
https://www.clublexus.com/forums/rx-...z-s-rx330.html
Plenty of info on the timing belt, I purchased my Lexus RX330 with 137,000 miles, I immediately replaced the timing belt & related parts.
Good thing, my timing belt was seriously cracked in many places.
I have traveled 10,000 since then with the Gates Kit with no problems at all.