Check the hose clips for tightness and examine the trunking for any cracks or splits and afterward all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best habit to locate a leak is to have the engine direction and hot and later spray lighter gas /propane or brake cleaner vis--vis each joint in turn. If the engine rev s going on you ve found your leak.
Might furthermore be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can accomplish a fast aberration find if you unplug the meter and control the engine without it. if the engine condition is the similar later chances are the meter or the association to it is faulty. Its also worth cleaning the MAF sensor wires, as they can get coated with dirt on top of grow old which later offsets the reading. Use some read cleaner or brake cleaner to spray onto the wires to remove the dirt upon no account touch the wires similar to everything as they are totally fragile
This could be a large vacuum leak ,with the MAF connected it is unaided measuring the expose that is getting later the MAF, as a result if the intake manifold is sucking in expose the let breathe 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. bearing in mind carb cleaner spray vaporizer in the place of the hissing in the same way as the engine admin and bearing in mind you hear the engine stall or rev later there is the leak ,could be a bad vacuum hose bad gasket upon the manifold.