Many repair manuals can be bought from online retailers or can be found online in digital form.

Try to pinpoint where the hissing noise is coming from. This will help you figure out where the leak is specifically.

The number of hoses your engine has and their locations vary widely depending on your specific engine. Use a flashlight while you are looking at your engine so that you can see as many areas as possible. Small cracks in a hose can cause a vacuum leak. A visual inspection may not be able to find this type of small leak.

Be sure that your engine is off and that it is cool to the touch when you do this. If a hose clamp moves, you should try to tighten it. Most hose clamps have a screw on them that tightens the clamp when you turn it. Even if you don’t find a loose or damaged hose, you could still have a vacuum leak. You will just have to look further for the source of the leak.

You may have to spray several times and in a variety of places to find the exact location of the leak.

A typical care has 17 to 20 inches (43. 2 to 50. 8 cm) of vacuum. If your hose is reading under that, it may have a leak.

In some cases, your mechanic will have a machine that allows them to use smoke to find the leak. They will surround the suspected problem area with smoke and look for areas where the smoke is being drawn into the engine. [8] X Research source

This is a relatively dangerous method to use for finding a vacuum leak. You are spraying a combustible material into your engine while it is running. In most cases, it will work fine and will not burn outside the engine. However, if there is a stray spark or overheated area, you could cause a fire on the engine or an explosion.

If your check engine light comes on, you should take your car to a mechanic. The mechanic can hook up a reader to your car that communicates with the car’s on-board computer. This will tell you specifically why the light turned on.

A high idle can be a symptom of other problems as well, such as a problem with your onboard computer or your throttle. [13] X Research source