How do you find a vacuum leak in a 1993 Toyota tercel?

1) use a smoke machine. Failing that:

2) let it sit with engine off for a long time, then start it cold and immediately spray all over the place with carb cleaner. If spraying a spot with carb cleaner makes a change in the sound of the engine suspect that area. Carb cleaner can damage paint and rubber.

3) Vacuum leaks often make a hissing noise. Also note that with a vacuum leak fuel trims tend to go rich (positive) at idle, if you have a scan tool that reads them.