I recently had to remove the airbox on my 99 RX300 and noticed that it was quite loose on the bracket even when I tightened the bolts down all the way. Looks like the rubber grommets/cushions/mounts have shrunk with age and need to be replaced, but I can't seem to find them in the Lexus parts catalog. The bolts are there, the rubber parts aren't. Anyone have any suggestions or sources for these?

 

I guess you could use rubber grommets Or you could use some self adhesive foam or rubber strip under the box to cushion it

Is it a problem?

 

These rubber mounts are some what special, and can be built with 2 rubber washer [top and bottom, same size] and a middle rubber grommet [thick washer] and a metal pass through [middle portion, you can cut standoff tubes or better still use the one from existing].

Make sure your engine mounts are good and there is no excessive movement of the engine block. These intake mounting are taking up the mechanical movement difference between the engine and the body. The other thing these moutings do is to do sound insulation from the intake to the body. Intake shell acts as a horn and mechanical waves need to be dampened. You have to wonder why did Toyota.Lexus create the shape of the intake with baffles in them.

Salim