Some makes (such as Ford) have explicit instructions NOT to clean the throttle body. THey have a thin coating that can be destroyed.

What about the RX300? Can I go to town cleaning it with Brake Cleaner? If not, what alternate cleaner to use?

 

Yes you can use a throttle body specific cleaner. TAPE THE STRAW TO THE CAN so it doesn't go for a ride into the intake.

 

And if you REALLY want a clean TB, remove it and bench clean it. I did this when I replaced my IACV a few years ago. I could not believe how much brown junk came out. One piece that came out was perfectly cylindrical, about 3/16 inches long. It had to be plugging up some orifice in the TB. Engine definitely ran smoother after this work. And yes, I used carb cleaner...a whole can of it.