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Car Care Advice

6 Common Vacuum Leak Symptoms (+Causes, Repairs, FAQS)

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A vacuum leak will decrease your car’s performance and driving ability, sacrifice your safety and lead to severe engine damage. While we’d love to say duct tape is the solution, you should get your vacuum leak repaired as soon as possible.

But what are the symptoms of a vacuum leak? 
And how is it caused?

This article will cover all that, including the possible auto repair costs for a vacuum leak, the diagnostic procedure, and more.

This Article Contains:

Let’s get started.

6 Common Vacuum Leak Symptoms

Fortunately, you can see vacuum leak symptoms from a mile away.

Here are six common symptoms you can’t miss:

1. Check Engine Light Comes On

Engine vacuum leaks almost always trigger the check engine light. 

While this won’t let you know you have a vacuum leak immediately, a quick scantool check may reveal a P0171 or P0174 code. The mechanic can then suggest the appropriate auto repair needed.

2.  Strange Engine Noises

Since engine vacuum leaks pull in air at high pressures, you’re bound to hear strange sounds from under the hood. You’ll likely hear squealing or hissing sounds from air sucking through cracks in the intake manifold gasket or vacuum hose.

Luckily, these sounds are hard to miss unless you play music a bit too loud.

3. Engine Performance Issues

When you have a vacuum leak, you’ll have excess air in your engine, compromising your air to fuel ratio. 

This means your engine vacuum compression in the combustion chamber is insufficient to create the needed power. This will increase engine speed and result in strain, causing engine performance issues.

In extreme cases, your engines vacuum leak can cause your car to stall while driving, which is very dangerous!

4. Backfires

Touching back on air to fuel ratios, a vacuum leak will likely make your engine run “lean” (too much air.)

This means the engine cannot efficiently ignite fuel in the combustion chamber. When fuel builds up in the cylinders and combustion occurs, it will expel a backfire.

Note: Backfires happen for various reasons, but it’s a good idea to get your engine checked out when they do or when you notice an illuminated check engine light.

5. Rough Idle

A rough idle is a key sign of a vacuum leak. With excess air in your engine, your car will be working overtime to create power. This will cause revs (RPMs) to bounce up and down on the tachometer, and you’ll experience excessive vibrations when your car is idle. 

If a rough idle symptom is left ignored, it can damage your engine internals. 

6. Black Exhaust Smoke

We hate to break it to you, but your car is not a smoke machine.

However, black smoke coming from your exhaust could indicate a vacuum leak.
When your engine has an improper air to fuel ratio, cylinder combustion levels will be insufficient, leading to black exhaust smoke.

Now that we’ve covered the symptoms of a vacuum leak, let’s go over its causes.

5 Reasons You Have A Vacuum Leak

Vacuum leaks are commonly caused by general wear and tear of components. But sometimes, installing faulty parts can also cause a severe vacuum leak.

Here are five possible reasons behind a vacuum leak:

1. Worn Or Broken Vacuum Hose

A vacuum hose (also called a vacuum line) helps maintain the correct pressure levels in the engine. Since vacuum hoses are made from rubber, the extreme heat coming from the engine can cause them to wear — and become brittle.

A brittle vacuum line is likely to split or tear, resulting in a vacuum hose leak. Vacuum hoses should be the first part you check when locating an engine vacuum leak.

Look on the bright side.
A leaking vacuum hose is cheap to replace and is far less concerning than a cracked intake manifold.

2. Cracked Air Intake Manifold

Although unlikely, an intake manifold vacuum leak shouldn’t be ruled out completely.

Extreme pressure, strain, or overheating can crack an intake manifold. This allows air to leak into the engine without passing through the throttle body.

When air doesn’t pass through the throttle body or mass air flow sensor and goes straight into the engine, there’s more air and less fuel to burn. This can potentially cause overheating and engine damage.

The good news?
An intake manifold vacuum leak is easy to spot.

The bad news?
Duct tape won’t fix this one.
An intake manifold vacuum leak is costly to repair. Let’s hope a faulty air intake manifold gasket causes the engine vacuum leak instead.

3. Faulty Intake Manifold Gasket

An intake manifold gasket seals the casing of the intake manifold, maintaining pressure inside the engine. 

An intake manifold vacuum leak can be caused by a gasket leak, either by general wear and tear or by a manufacturing error. Either way, you’ll want to replace it as soon as possible. 

A faulty intake manifold gasket is a bit trickier to pick up and will require a thorough diagnostic to locate it. 

4. Faulty Brake Booster Diaphragm

A brake booster uses the engine’s vacuum pressure to amplify your foot power to the brakes. 

If a brake booster diaphragm is faulty or ruptured, air can leak in. This directly affects the vacuum system, decreasing the pressure inside the engine.

Driving with a faulty brake booster is extremely dangerous!
Besides having insufficient power from your engine, you’ll find it pretty hard to stop the vehicle on your own.

Bottomline — examine your car if you notice any braking or engine performance issues.

5. Faulty EGR Valve

The EGR valve (exhaust gas recirculation) connects to the intake manifold and sends a small amount of exhaust gases back into the engine cylinders. This controls nitrogen oxide emissions in cars.

When an EGR valve is faulty or cracked, it can allow unmetered air to be sucked into the engine. 

Unmetered air will affect your car’s air to fuel ratio and engine pressure, leading to:

If you suspect a vacuum leak, the next step is to diagnose where the leak is coming from to get the necessary auto repair. 

Let’s see how this is done.

Diagnosing A Car Vacuum Leak and Possible Repairs

The diagnostic procedure for locating an engine vacuum leak is simple.

Here’s how mechanics find your engines vacuum leak:

Step 1. The Water Method 

A cheap but effective way to locate a severe vacuum leak is using the water method.

While the car is running, a mechanic will use a water spray to douse suspected fault sights for a vacuum leak. These sights include the intake manifold, intake hose, vacuum hose, and EGR valve.

Water will be sucked into the leak when water is sprayed on it, indicating where the leak is.


Note: Small amounts of water won’t damage the engine when sucked in.

Step 2. Carb Cleaner Test 

An experienced mechanic will likely try the carb cleaner method if the water method proves ineffective.

They’ll spray suspected fault sights as they did with the water test. 

If the carburetor cleaner is sucked into the leak, the car’s engine performance at idle will improve temporarily. That’s because a carburetor cleaner is combustible and will compensate for the low air to fuel ratio caused by the vacuum leak.

Step 3. Test The Brake Booster

If the water and carb cleaner tests reveal no vacuum leaks around the engine, then the brake booster is the likely culprit.

To test the brake booster for a vacuum leak, a mechanic will start the engine and turn it off after around 15 seconds. This will allow some vacuum pressure to build up in the engine.

The mechanic will then press and release the brake pedal several times. If the brake pedal has no resistance or behaves strangely, it’s a clear sign of a vacuum leak.

Repairs And Cost Estimates

For reference, here are some cost estimates for repairs:


Note: Labor charges may vary based on your car model and your location.

Now that you have a clear understanding of a vacuum leak, let’s answer some related questions.

2 Vacuum Leak FAQs

Here are the answers to two vacuum leak FAQs you might want to know: 

1. How Do I Prevent A Vacuum Leak?

Unfortunately, you can’t really avoid vacuum leaks — only delay them from happening.
The best way to delay a vacuum leak is by regularly maintaining your engine and intake manifold. 

A few vacuum leak-orientated ways you can keep your engine maintained are:

2. Is It Okay To Drive With A Vacuum Leak?

It’s not advised to drive with a vacuum leak unless absolutely necessary.

Aside from the dangers of having your car stall while driving, a vacuum leak can cause severe damage to your engine’s internals. This will lead to further costly repairs down the road.

It’s best to fix a vacuum leak as soon as it’s detected.

Closing Thoughts

A vacuum leak can seem like a minor issue at first, but it can lead to major car troubles.

While essential maintenance and care for your car can possibly prevent vacuum leaks from occurring, you need to repair it as soon as you suspect you have one. Doing so will turn your car from a smoke machine to a driving dream!

But who do you contact when you have a vacuum leak?
RepairSmith!

RepairSmith is a convenient mobile vehicle auto repair and maintenance solution
We offer competitive, upfront pricing with easy online booking, and all repairs come with with a 12-month | 12,000-mile warranty.  

Contact RepairSmith for an accurate cost estimate of your vacuum leak repair, and our expert mechanics will get it done right in your driveway!