Check the hose clips for tightness and inspect the trunking for any cracks or splits and then all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best way to locate a leak is to have the engine direction and hot and later vaporizer lighter gas /propane or brake cleaner going on for each joint in turn. If the engine rev s occurring you ve found your leak.
Its also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a ill pump will all repercussion in insufficient fuel beast delivered to the engine. Might plus be worth cleaning out the idle enthusiasm direct motor / valve as these get clogged stirring when carbon and some brake cleaner washed through helps forgive things off.
This could be a large vacuum leak ,with the MAF united it is without help measuring the let breathe that is getting when the MAF, so if the intake manifold is sucking in expose the air to fuel ratio will be extremely out and cause the engine to stall. If MAF is disconnected the engine goes into a limp measurement and lets the engine run. as soon as carb cleaner spray can spray in the area of the hissing gone the engine direction and similar to you hear the engine stall or rev superior there is the leak ,could be a bad vacuum hose bad gasket upon the manifold.