Symptoms and how to test for intake manifold leak? new for 2022

One of the most common problems on vehicles is intake manifold leak. Intake manifold leak can lead to a variety of problems such as decreased fuel economy, poor performance and emissions, and knock.

Symptoms of intake manifold leak can be difficult to detect, and can even go unrecognized for a long time. However, by following a few simple steps, you can easily test for intake manifold leak and determine the best course of action.

This post will answer your question about “how to test for intake manifold leak” and provide relevant information.

how to test for intake manifold leak
how to test for intake manifold leak


What exactly is an induction manifold gasket?

What exactly is an induction manifold gasket?
What exactly is an induction manifold gasket?

The intake manifold gaskets sit between the cylinder head and the intake manifold, and their main purpose is to prevent leaks. Over time, they can slowly degrade, which can lead to a leak.

If a leak occurs, the gasket should be replaced as soon as possible to prevent damage to the engine or getting stranded.

Symptoms of an Intake Manifold Leak

Symptoms of an Intake Manifold Leak
Symptoms of an Intake Manifold Leak

Intake manifold leak symptoms may include:

  • Coolant leaking outside the intake manifold
  • Poor acceleration
  • Hard starting
  • A check engine light
  • Rough idle or engine operation
  • Hesitation
  • Rich or lean stumble
  • Backfiring
  • Engine overheating
  • Increased emissions
  • Increased fuel consumption

The intake manifold directs outside airflow and injected fuel into each cylinder as needed for combustion.

In modern fuel-injected engines, the electronic control unit (ECU or car’s computer) adds the correct amount of fuel to the combustion chamber based on engine operating conditions.

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The engine’s computer monitors the amount of air entering the engine and maintains a balance between 14 parts of air and 1 part of fuel, ensuring proper operation.

A leak in the intake manifold can upset this delicate balance and create a performance issue.

A leak may occur for more than one reason, such as a break in the pipe or an opening in the tank.

  • Vacuum hose disconnected
  • Vacuum hose damage
  • Intake manifold gasket damage
  • Intake manifold damage
  • unsecured intake manifold bolts

Some leaks are easier to diagnose than others.

It is a good idea to have the repair manual for your specific vehicle on hand in case you need to identify and locate components. If you don’t have this manual yet, you can find a relatively inexpensive copy on Amazon.

Here’s How To Find Vacuum Leaks

Here’s How To Find Vacuum Leaks
Here’s How To Find Vacuum Leaks

We have laid out the tests in a step-by-step fashion so that you can find the problem quickly. Throughout these tests, all procedures will lead to finding the same issue.

Smoke testing is a common way to verify the functionality of electronic devices. Some methods for doing this include checking continuity, using a multimeter, and testing with an oscilloscope.

Let’s do this!

  • In order to locate all of the vacuum lines, tubes, and components on an engine, you will need to find information about where they are located. If your car does not have a label under the hood that indicates where these lines are situated, you can likely find this information online or in your owner’s manual. Additionally, if the engine has been modified it may require additional research in order to identify which lines have been altered.
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  • In order to inspect the lines and connections, visually examine them all for any apparent issues. If there are any problems, such as a disconnected line or broken connection, then it will be evident.

Rotted vacuum cap on Holley carb that’s ready for replacement., Hank O’Hop

  • Sometimes, vacuum leaks exist within complex circuits and systems that are difficult to access. For example, a faulty brake booster can create a vacuum leak, and you will not be able to determine this simply by looking. The good news is that the device you use to bleed your brakes can be used. All you have to do is connect it to the vacuum lines, pump it up and observe the reading. If it holds a vacuum, you can eliminate this as one of your possible causes and continue testing other areas of the system
  • If you notice any vacuum leaks, it may be time to have your intake manifold inspected. Make sure there are no cracks or damage present or on the throttle body or carb, and look for any vacuum sensors on the manifold to ensure that they’re intact.
  • If you suspect a vacuum leak, your first step is to spray water over the suspected area. This will cause the air to escape and you’ll be able to see where the leak is.
  • One way to detect manifold and vacuum leaks is to use a propane torch. Just open the propane valve without igniting it, run the tip along various gasket locations or vacuum connections, and listen for an idle spike.

Introducing propane to manifold gasket on 440. The same procedure applies to any engine., Hank O’Hop

  • The carb cleaner test is a procedure that closely resembles the propane enrichment test. You’re introducing a flammable substance to each connection, and the process is pretty much the same. All you need to do is identify where the gaskets are and spray some carb cleaner while listening to engine speed. If you perform this test, be careful—the stream of carb cleaner isn’t as controlled as using propane.

The Consequences of a Multiple Leak

The Consequences of a Multiple Leak
The Consequences of a Multiple Leak

A carburetor manifold leak can cause an engine to run lean, because the air that leaks into the mixture introduces too much air and fuel. This excess air generates more heat, which raises the engine temperature and idle speed.

Leaks that are smaller in magnitude will usually have a minor impact on the motorcycle’s performance and reliability. On the other hand, larger leaks can cause the air/fuel mixture to lean out of balance, which can lead to overheating and severe engine damage.

Detecting Multiple Leaks

Detecting Multiple Leaks
Detecting Multiple Leaks

Start your motorcycle and let it idle until you can recreate the problems that you are experiencing. Spray a generous amount of penetrating oil onto the manifolds between the carburetors and the air box, one at a time, and listen for any changes in engine idle speed.

If the idle speed suddenly decreases, this could be an indication of a leak in one of the engine’s manifolds. If there is no change in the idle speed, spray some penetrating oil between the engine and carburetors to identify where the leak is. Once you have found and fixed the source of the leak, restart your engine and see if it goes back to its normal idle speed.

Cost of Replacing an Intake Manifold Gasket

Cost of Replacing an Intake Manifold Gasket
Cost of Replacing an Intake Manifold Gasket

The intake manifold gasket is a costly part of a car due to its durability requirement and unique shape. A new replacement gasket will likely cost between $50 and $120, which isn’t too bad.

Intake manifold gaskets can be quite expensive to replace, costing anywhere from $250 to $500 in labor.

On average, you can expect to pay around $300 to $620 for the total cost of an intake manifold gasket replacement.

Intake Manifold Leak Troubleshooting

Intake Manifold Leak Troubleshooting
Intake Manifold Leak Troubleshooting

If your engine has aluminum cylinder heads, you may experience corrosion around the ports of the coolant. The intake manifold gasket’s seal bead may also be eaten away, leading to leaks.

If you notice this symbol, it means the seal on the container will not hold and is therefore likely to leak.

If you notice an intake manifold leak, don’t try to fix it yourself. Most times, a professional mechanic is better equipped to handle the job. However, here are some steps you can take if you determine that your engine is leaking air:

Testing for Coolant Leaks

If there are coolant leaks on the outside of the gasket, you can see them with your eyes. But if there are internal leaks which cause the coolant to flow into the oil or combustion chamber, then you won’t be able to spot them that easily.

It is important to inspect your system regularly for signs of contamination and to pull the codes if necessary in order to diagnose the problem.

If the codes relate to the oxygen or efficiency sensor, it means that there has been an issue with coolant getting into the combustion chamber. Since phosphates are found in the coolant, along with other chemicals, this will cause damage to these components.

If you have a V8 or V6 engine, you can use the codes to figure out which bank has the leak. Any big leaks that are in the runner may give you a misfire code. If you experience this problem for extended periods of time, take out all of your spark plugs in your vehicle.

If there are white deposits on the electrodes, this may be a sign that there is a leak in the cooling system. Leak checks such as leak down checks and compression checks should be performed to determine where the leak is coming from.

Testing for Air Leaks

If you have a fuel trim problem, it may be due to a vacuum leak. If you can find the leak, it will be much easier to correct.

If air leaks into the engine through the intake manifold, then it will cause air to be drawn in instead of pushed out, which can impact the emissions system and the engine itself.

If you have a smoke machine, then it is easier to diagnose leaks because the intake manifold will become pressurized and vapor and smoke will be drawn out.

Attach the smoke machine to the vacuum port and ensure that you have the right sized plug when blocking the throttle body. Block off both PCV systems as well.

If the PCV system or oil filter is emitting smoke, it may mean that there is a crack or leak underneath the intake manifold. Additionally, it may mean that the valve seals or guides are too worn out to function properly.

Potential leaks and how to test for intake manifold leak

Potential leaks and how to check
Potential leaks and how to check

1. Leaks in the Intake Manifold Vacuum Hose

Vacuum hose leaks are a common culprit of intake manifold leaks.

  • It is important to disconnect the vacuum hose while servicing, repairing, or replacing an engine component in order to avoid potential injury.
  • It’s not uncommon for vacuum hoses to wear out after thousands of miles of use in harsh conditions, such as pressure, high temperatures and oil spills.

To check for a leaking hose:

  • The vacuum hose diagram typically shows the routing of hoses connected to vacuum-controlled components. If necessary, you can visually check each hose for obstructions or damage.
  • With your fingers, feel along the hose for any areas that are rough or too soft. If you find any of these spots, it may be a sign that the hose is failing or has leaked.
  • If you want to connect the end of the hose to a faucet, make sure that the hose is properly connected at both ends. You may need a telescopic mirror for hard-to-reach places.

If you see bubbles forming around the leak, you have found it.

To fix a rough idle, you can use starting fluid to fill any leaking areas in the engine. This will help to smooth out the idle and make it run more smoothly.

2. Intake Manifold Gasket Leaks

The intake manifold attaches to the cylinder head with a gasket in between to create a seal.

The air intake system on most engines blocks outside air from entering the engine. This prevents unmetered, outside air from entering the engine, and it also prevents coolant or oil from leaking out of the cylinder head or entering the combustion chambers.

To check for an intake manifold external leak:

In order to diagnose a leak, it can sometimes be easier to check for a gasket that is leaking air or coolant outside of the intake manifold.

  • The intake manifold is a device that directs air and fuel to the cylinders in a engine. It is located near the carburetor or throttle body. The manifold usually has several ports, and it may also have valves that allow air to enter or leave the engine. A visual inspection of this area can help determine if there are any problems with the engine’s performance.
  • Using your hand, feel around those areas where you can’t visually inspect. If necessary, use a telescopic mirror to get a better view. Pay attention to any sounds the object may make.
  • Put one end of the hose against your ear and use the other to trace where it connects with the throttle body. If you hear a distinctive hissing sound coming from the gasket area, this is a sign of a leaking gasket.
  • If you notice a change in the idle speed or smoothness of the engine’s idle, it may be indicative of a leaky area around the gasket.

To check for an intake manifold internal leak:

Leaks from within the engine are always cause for concern, but internal leaks caused by a damaged gasket, cracked intake manifold or cylinder head can be more serious and need to be diagnosed and fixed as soon as possible.

If you are noticing a loss of coolant, and can’t seem to find a leak, it is important to take your car in for diagnostic work before the problem becomes more costly. If there is an internal coolant leak into one of the engine cylinders, this can cause severe damage and even result in an engine failure.

3. Damaged Intake Manifold Leaks

Vehicles with aluminum cylinder heads and plastic intake manifolds are more likely to experience coolant leaks. This can lead to corrosion, which can eat away at the plastic around the intake ports.

The plastic intake manifolds are more likely to develop cracks than those made from aluminum.

You still can try using a piece of rubber hose as a diagnostic tool:

  1. Put one end of the hose against your ear.
  2. Use the other end of the hose to trace around the intake surface, cylinder head or block areas.

If you notice a coolant leak, take your vehicle to a garage for proper diagnostic work. This could mean that the cylinder is damaged and requires replacement.

One way a car technician can identify and fix hard-to-find intake manifold leaks is by using a smoke machine. In this video, you can see how the technician uses the machine to detect where the leak is coming from

4. Diagnosing Leaks With a Vacuum Gauge

If you suspect a vacuum leak, you can try to find it using a vacuum gauge. If the leak is hard to spot, your local auto parts store may loan you one.

  1. Warm up the engine.
  2. Connect the gauge to a vacuum port on the intake manifold in order to measure engine vacuum.
  3. Set your transmission to Park (automatic), or Neutral (manual).
  4. Engage the emergency brakes.
  5. Start and let the engine idle.
  6. An engine in good mechanical condition will typically read between 17 and 21 inches of mercury (Hg) at sea level. For every 1000 feet of altitude after the first 2000 feet, subtract 1 Hg from this range.
  7. If your blood pressure machine’s needle fluctuates between 3 and 9 in-Hg below the normal reading, it is likely that the intake manifold is leaking vacuum.

Make sure to check every vacuum hose if you suspect a leak, and also investigate any cracks or damage on the intake manifold.

If your car has a two-part intake manifold–the upper and lower sections that come together to form the engine’s breathing apparatus–a leak can manifest in different ways.

  • If there is a problem with the intake manifold, it can result in a leak. This could be either from the gasket or from damage to the manifold itself. If the manifold is cracked, then leakage will occur.
  • If your car’s upper intake manifold has a problem, such as a leaking gasket or cracked manifold, it will develop a vacuum leak.
Trouble codes stored in your computer's memory can help you diagnose the source of a vacuum leak

Trouble codes stored in your computer’s memory can help you diagnose the source of a vacuum leak

5. Pay Attention to the Check Engine Light

An intake manifold leak can be difficult to identify, and a check engine light can help in this situation.

If the check engine light comes on, perform a system check to determine the source of the problem. This may lead you to resolving it sooner than you expected.

What if My Engine Doesn’t Power Vacuum-Operated Systems?

What if My Engine Doesn't Power Vacuum-Operated Systems?
What if My Engine Doesn’t Power Vacuum-Operated Systems?

Your car might not have any options like a power brake system. This could be because the previous owner removed them, or because the engine build doesn’t create enough vacuum to power those components.

A lot of modern engines even feature a belt-driven vacuum pump to help the brake system.

If no vacuum lines are coming off the engine, only faults between the intake system’s mating surfaces or components themselves can be the source of a vacuum leak. To inspect these surfaces, you may want to implore tests listed above if there is no obvious damage.

If your auxiliary vacuum pump is not working properly, it won’t cause any problems with the engine running. However, only systems that are using that auxiliary vacuum power will suffer.

For example, if the connection between the power brake booster is the problem, then your brakes will be as hard as a rock because there’s not enough vacuum to assist the system.

When inspecting a vacuum-powered system, it’s usually necessary to inspect the system visually as well as using the vacuum pump test. However, if there are indications that the vacuum pump test is not revealing any problems with the system, then you may need to take further action.

What about Induction by Force?

What about Induction by Force?
What about Induction by Force?

If your car has a turbocharger or supercharger, it will instead use positive displacement pumps (superchargers or turbochargers) to force air through the intake system.

It can be easy to overthink the scenario and conclude that the steps listed above won’t work for your setup. And to an extent, that is true. Finding leaks in a forced induction system requires special testing tools and procedures.

Supercharging a car’s engine does not change the level of vacuum that is produced at idle; it only alters how much power the engine can produce. The same procedures can be used to test a supercharged car’s engine as you would an unsupercharged one.

When You Need a Certified Mechanic

When You Need a Certified Mechanic
When You Need a Certified Mechanic

For some people, DIY car repairs can be risky and difficult. Sometimes, you need reliable car repair work done by professionals who you can trust to do a good job. Our partners at Goodyear Tire & Service are certified mechanics who know how to fix cars correctly and safely.

Pro Tips for Detecting Vacuum Leaks

Pro Tips for Detecting Vacuum Leaks
Pro Tips for Detecting Vacuum Leaks

Here are The Drive’s pro tips.

  • If you notice a significant noise coming from under the hood of your car, it might be indicative of a vacuum leak. This type of leak can be quite noisy, and may even produce a whistling sound. If you locate the source of the leak, it might be easy to fix.
  • If the vacuum gauge test is not conclusive, you can try to pinch the vacuum lines by hand while the engine is running. This will help you determine which component is causing the low idle.
  • If you have recently installed an intake manifold and are experiencing start and run issues, make sure that it is on tight.
  • When performing propane enrichment or carb cleaner tests, be careful not to introduce flammable gases under the hood of a running car. These tests are very conclusive, but can lead to a fire if done incorrectly.
  • Carb cleaning isn’t limited to using carb cleaner – any flammable liquid will do.
  • A propane enrichment test is typically preferred over a carb cleaner test because it allows for more precise control of the flow of propane gas. This is particularly beneficial in tight spaces, where a flexible hose can be attached to the nozzle for even greater precision.

F.A.Q about “how to test for intake manifold leak”

How do you know if your intake manifold is leaking?

If you notice any of the following signs that your car’s intake manifold may be leaking, it’s best to take it in for repairs: a decrease in engine performance, CEL (Check Engine Light) activation, or an increase in vehicle noise.

  1. Improper air-fuel ratio.
  2. Overheating.
  3. Engine misfires.
  4. Decreased acceleration.
  5. Poor fuel economy.
  6. Coolant leaks.
  7. Milky engine oil.
  8. Backfires or rough idling.

What can be used to detect a vacuum leak at an intake manifold gasket?

The vacuum leak detection machine sends smoke into the engine’s intake manifold and looks for any signs of smoke seeping out of hoses, gaskets, or cracks in the manifold. If there is a leak, it will be evident by the presence of smoke.

How do you know if your intake manifold is cracked?

When the intake manifold is off the engine, pressure testing or using a penetrating dye may be the best way to determine if it leaks.

Can intake manifold leak cause low compression?

If the engine is leaking exhaust manifolds, it can cause damage to the engine valves. Once this damage is done, the only fix is a valve job.

What happens if your intake manifold is leaking?

A vacuum leak can cause problems with the engine’s air-fuel ratio, which can lead to misfires, a decrease in power and acceleration, a reduction in fuel efficiency, and even stalling.


By following these steps, you can easily test for intake manifold leak and determine the best course of action. If you are experiencing any of the symptoms listed above, don’t hesitate to take your vehicle to a mechanic for a more in-depth inspection.

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