Find the hissing sound lol. Check the obvious spots, like TB idle screw the seal on the idle screw tends to leak. place your finger over the hole and see if it alters the rev. Idle speed controllers can also be a problem when they burn out or jam or their plunger wears out or falls off. Im not sure if the construction of the 1g non turbo throttle bodies are identical to a turbo models tb. But those are problem areas forsure. Intake manifold gasket could leak from the bottom and that would be difficult to diagnose. Start in the easily accessible areas. Check around your injectors to be sure the seals arent leaking where they meet the head. they will be wet with fuel if they leak.\
this is just a start.
