Hello,

I have a problem in emission control system in my 1986 toyota tercel ( federal vehicles with 3A Engine ), so I need the under hood vacuum diagram to repair my car.

The aftermarket Haynes manual will provide the various vacuum hookups:

http://www.haynes.com/

If your vehicle uses an OBD 1 or OBD II diagnostics system, then you can pin-point the emissions failure (sensor or module) very quickly. In some older toyotas, your manual shows how to obtain a trouble code by hooking up a wire between 2 points in your under-hood fuse compartment. The engine light will flash thus providing a fault code which you can look up.