I use Propane to test for vacuum leaks (less messy than carb cleaner or other sprays). Take the nozzle tip off a propane torch and replace it with some snug fitting rubber hose about 2 feet long. Practice with the valve to get a moderate gas flow (not a roaring blast).

With the engine at a warm idle, open the gas valve and poke the end of the hose around each injector for a couple of seconds. If the seals leak, you should hear an RPM change when the propane gets sucked in and burned.

Do the same around any other suspected areas, like hidden vacuum hose ends and the intake manifold gasket itself.

To block the breeze from the fan, lay a piece of cardboard from the fan shroud to the engine.

Also, remove the air duct between the AMM and the throttle body, and check it carefully for cracks in the accordian pleats, especially on the underside. Electrical tape can make a temporary repair if leaks are found.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.