Check the hose clips for tightness and inspect the trunking for any cracks or splits and as well as every the vacuum system, the little bore pipes and fittings for cracks and missing parts. The best artifice to find a leak is to have the engine management and hot and then spray can lighter gas /propane or brake cleaner roughly speaking each joint in turn. If the engine rev s occurring you ve found your leak.
Might as well as be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can pull off a quick irregularity locate if you unplug the meter and manage the engine without it. if the engine condition is the same next chances are the meter or the connection to it is faulty. Its as well as worth cleaning the MAF sensor wires, as they can get coated once dirt exceeding become old which after that offsets the reading. Use some entre cleaner or brake cleaner to spray onto the wires to surgically remove the dirt upon no account be adjacent to the wires bearing in mind all as they are totally fragile
This could be a large vacuum leak ,with the MAF associated it is solitary measuring the air that is getting with the MAF, as a result if the intake manifold is sucking in air the freshen to fuel ratio will be very out and cause the engine to stall. If MAF is disconnected the engine goes into a limp measurement and lets the engine run. taking into consideration carb cleaner vaporizer spray in the area of the hissing considering the engine organization and as soon as you listen the engine stall or rev later there is the leak ,could be a bad vacuum hose bad gasket on the manifold.