How do you see if there is a vaccum leak?

To check for a vacuum leak, start by visually inspecting hoses and connections for any cracks, breaks, or loose fittings. You can also listen for hissing sounds while the engine is running, which may indicate escaping air. A more thorough method involves using a smoke machine to introduce smoke into the vacuum system; any smoke escaping from a leak will be easily visible. Additionally, monitoring the engine's idle speed and performance can provide clues, as a vacuum leak often results in a rough or fluctuating idle.