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How to find a vacuum leak
Consult the vacuum diagram of your engine.
In order to understand where your engine's vacuum hoses are and what areas might be leaking, you can look at a diagram that details how the vacuum system works. These diagrams can typically be found in repair manuals made for your specific make, model, and year of car.
Many repair manuals can be bought from online retailers or can be found online in digital form. Start the car and listen for a hissing sound.