Check the hose clips for tightness and inspect the trunking for any cracks or splits and after that all the vacuum system, the little bore pipes and fittings for cracks and missing parts. The best pretension to locate a leak is to have the engine dealing out and warm and after that vaporizer lighter gas /propane or brake cleaner around each joint in turn. If the engine rev s happening you ve found your leak.
Its after that worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a not at your best pump will every result in insufficient fuel being delivered to the engine. Might in addition to be worth cleaning out the idle promptness direct motor / valve as these get clogged up behind carbon and some brake cleaner washed through helps forgive things off.
This could be a large vacuum leak ,with the MAF related it is only measuring the air that is getting as soon as the MAF, consequently if the intake manifold is sucking in ventilate the air to fuel ratio will be enormously out and cause the engine to stall. If MAF is disconnected the engine goes into a limp measurement and lets the engine run. when carb cleaner vaporizer spray in the area of the hissing afterward the engine organization and next you hear the engine stall or rev well ahead there is the leak ,could be a bad vacuum hose bad gasket upon the manifold.