The idler arm is the right side counter part to the steering arm. It is stricktly a slave device. It connects to the passenger side of the drag link(aka center tie rod) You mentioned the trans mount, if you have vibration problems the motor mounts would be a good bet also. And I believe there are upper and lower ball joints.

The control arms also have bushings, fixed uppers and eccentrically adjustable lowers. You would need a spring compressor to replace these.

Front ends have four specs- in a nutshell

Toe-in- pigeon toed- tie rods
Toe-out - duck feet- tie rods
castor and camber- bow legged or knock-kneed- lower arm eccentric bushings for adjustment but bad ball joints can affect this

this is not Gospel but a rule of thumb. If there is anyone more knowledgable please chime in.