1. Visual Inspection

Before testing, check for cracked, disconnected, or brittle vacuum hoses. Pay close attention to areas near heat sources and where hoses connect to intake components.

2. Soapy Water Spray (Safe & Simple)

• Mix water with dish soap in a spray bottle.
• Spray it around vacuum hoses and intake gaskets while the engine is idling.
• If there’s a leak, the idle may change, or you’ll see bubbles forming where air is escaping.

3. Propane Test (Careful with this one!)

• With the engine idling, use an unlit propane torch or a can of carb cleaner.
• Slowly move it around suspected leak points (intake manifold, throttle body, vacuum lines).
• If the idle surges when propane is introduced, you’ve found the leak.
  ⚠️ Be cautious! Propane is flammable. Do this in a well-ventilated area.

4. Carb/Brake Cleaner Spray (Similar to Propane Test)

• Spray a small amount of carb or brake cleaner around vacuum connections.
• If the engine RPM changes, there’s likely a leak in that area.
  ⚠️ Be extra careful—carb cleaner is highly flammable!

5. Smoke Test (Most Effective & Professional Method)

• A smoke machine forces smoke into the intake system.
• Smoke will escape from any vacuum leaks, making them easy to find.
• Some DIY methods use a cigar or a homemade smoke canister, but a proper smoke machine is best.

6. Using a Vacuum Gauge

• Connect a vacuum gauge to a vacuum port on the intake manifold.
• A healthy engine should show steady vacuum (typically 17-22 inHg at idle).
• Fluctuating or low vacuum may indicate a leak.

7. Using an OBD2 Scanner (For Modern Cars)

• If your check engine light is on, scan for codes like P0171 (Lean Condition) or P0507 (High Idle RPM).
• Live data showing high Long-Term Fuel Trim (LTFT) may also suggest a vacuum leak.

Best Method?

If you have access to a smoke machine, it’s the fastest and safest way to detect leaks. If not, the carb cleaner or propane method works well but requires caution.