If your vehicle is showing loud sucking or vacuum noise while the engine is idling, here are the most likely causes and the parts you'll need to fix each one.
Rubber vacuum hoses become brittle from engine heat and can crack, or they are frequently knocked loose during routine maintenance like air filter replacements, creating a direct path for unmetered air to be sucked into the engine.
The gasket sealing the intake manifold to the engine block can degrade over time or be pinched if recently replaced, allowing a large amount of air to be sucked in and causing a rough idle.
The Positive Crankcase Ventilation (PCV) valve regulates crankcase pressure. If its internal spring or diaphragm fails, it can pull excessive vacuum, resulting in a loud hissing or sucking noise.
If the throttle body was recently removed for cleaning, reusing an old gasket or failing to torque the bolts correctly will cause a vacuum leak right at the intake opening.
The power brake booster uses engine vacuum to assist braking. If its internal rubber diaphragm tears, it creates a massive vacuum leak and usually causes a very stiff brake pedal.
The EVAP purge valve routes fuel vapors into the intake manifold. If it gets stuck open or its plastic housing cracks, it acts as a vacuum leak.