How to Check Engine Vacuum Hoses

Reviewed by Charley Helvy

Last Updated: December 9, 2023 References

Knowing what faulty vacuum hoses look like is an important part of keeping your car in good condition. Many of these hoses control your car's idle, emissions components and environmental controls such as your heat. This article will tell you how to check engine vacuum hoses.

Method 1

Method 1 of 2:

Visual and Hands-On Inspection

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Check each hose for bulges and swelling. If a hose feels soft or spongy when you touch it, this can indicate damage caused by your car's oil.^{[1]
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- A swollen hose that is cracked and hard is often caused by heat damage. These hoses can be too close to heat sources under the hood or it may be the result of overheating.
- Bulging hoses can also be caused by electrochemical degradation when there's a coolant leak dripping onto hoses. Sometimes you can feel tiny cracks or weak spots when you squeeze a cool hose near one of the ends.
Small parallel cracks in the cover of a hose can be ozone damage. Scratches and other irregular injuries to the hoses can be caused by hoses rubbing against a moving part of the engine.^{[2]
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Method 2

Method 2 of 2:

Using a Vacuum Detector

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Attach your vacuum gauge and start your vehicle's engine. Allow your car to idle for a couple of minutes. Your gauge should read between 14 and 18 inches of vacuum.
- If the reading is low or non-existent, there's a blockage or leak in the vacuum line. Visually check the entire length of the hose for the problem.

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Question

My truck has a rough idle but when I remove the vacuum line it smooths out. Why is this?

Community Answer

It depends on what part it is. On my 1999 Ford Ranger 4.0 V6 I had to replace the canister purge valve and I had almost the same situation. When you open the hood it should show a diagram with the vacuum hoses and the various places they go to. On mine it's the charcoal bed to the canister purge valve then to the throttle body. It wouldn't be the IAC so no worries there. It mainly depends on what truck it is.

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How long can I drive with a faulty vacuum hose?

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You can drive it, but not repairing it will ruin your fuel economy and create possible damage to an expensive catalytic converter.

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I accidentaly disconnected when cleaning my car and was confused as to where to connect the vacuum hoses for my LN130 Toyota turbo engine. Can anybody help me?

Community Answer

Look on the top of your engine for a small disc object (might look like a flying saucer). There should be a small tube on the top of it. See if you can fit the vacuum hose back on tube.

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Tips

Some leaks are not visible during the visual inspection. In these cases, using a vacuum detector in conjunction with a hands-on examination can be useful.

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If you are unable to locate a suspected leak, take your vehicle to a mechanic's shop where there's more sophisticated detecting equipment.

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A hissing or vacuum sound can sometimes be heard if the leak is big enough.

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