Inspect all vacuum hoses for cracks, splits, loose fittings, and disconnected lines
Check intake manifold gaskets, throttle body gasket, and vacuum ports for leaks
Listen for hissing sounds around the engine while it is idling
Spray carburetor cleaner or brake cleaner around suspected leak areas and watch for RPM changes
Use a smoke machine to introduce smoke into the intake system and look for escaping smoke
Check fuel trims with an OBD2 scanner for signs of a vacuum leak
Inspect the PCV valve and related hoses for damage or blockage
Test brake booster and vacuum reservoir lines for leaks
Verify the intake ducting between the air filter and throttle body is sealed properly
Perform a vacuum gauge test to check for abnormal readings
Use soapy water on accessible vacuum connections and look for bubbling
Check for rough idle, high idle, stalling, or lean codes that may indicate a leak