In my 2000 RX300, I have an aftermarket front motor mount (a Westar). I changes the rear mount to a Toyota unit. THe vehicle still idles rough.

This is the mount which is hydraulic and uses a VSV (Vacuum Switching Valve). Visually the Westar mount looks healthy. But I dont know if it even has hydraulic oil in it or it is solid. Is there any way to test it?

 

Rev the engine see how much the motor moves the engine will sag if this is required.

 

There are two purpose of the mount.
1. Standard provides a mechanical support, but also provides a give in movement without slop. This is the standard use of engine mount and if you use strong and long levers you should not be able to observe any play (wear or break in the rubber isolation).

2. Smart mount which produce reverse push in the direction of the movement. Only way to test that would be with giving controlled input and see the engine mount end move. How can one produce the right signal input and measure the movement, is not easy to create and establish. It would most likely be cost prohibitive (research time to establish movement+ generation of signal + measurement) and not worth pursuing. (imho).

I would limit my effort to item #1 and assume #2 is good. Replace the mount if #1 is bad.

As a suggestion I would also look at other causes of engine vibrations. Is your rpm pretty stable and around 750. Also check the other mounts.

Salim