Dan Ferrell writes about do-it-yourself car maintenance and also repair. He has certifications in automation and also control technology.

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A vacuum leak can cause a myriad that drivability problems, together it introduces extra, unwanted air right into the engine, leaning the end the air/fuel mixture. Modern-day internal combustion (multi-port fuel injection) engines use intake vacuum to operate sensors, actuators, and power brakes (on some vehicles). Older engines also use the to operate some emission manage devices and to traction fuel right into the combustion chamber.

So even a little vacuum leak deserve to trick you, and your auto computer, into believing a details sensor or system needs fixing. Then you start replacing contents hoping you'll solve the problem, unsuccessfully.

Often, a vacuum leak renders an audible hissing sound, which makes it easy to find; various other times, though, you won't hear anything. Auto shops usage special, costly equipment to detect difficult to uncover leaks. But prior to you head come the shop, you can apply basic techniques provided to track most usual vacuum leaks.

This overview not only helps you discover a vacuum leak or one obstructed vacuum hose and gives you beneficial repair tips, yet it additionally tells you what engine performance problems may allude to a potential vacuum leak. Therefore let's begin there.


I. When need to I Troubleshoot for a Potential Vacuum Leak?

Vacuum Leak Symptoms

Vacuum Leak associated Trouble Codes

II. Just how to uncover a Vacuum Leak

Using a Vacuum Gauge

III. Checking the intake Manifold because that Vacuum Leaks

IV. Making use of a Hand Vacuum Pump to Test gadgets for Vacuum Leaks

V. Vacuum water tap Repair Tips


Throttle body and also intake manifld gaskets can build leaks together well.

Photo courtesy that James A O top top Flickr.

I. When must I Troubleshoot because that a Potential Vacuum Leak?

Vacuum hoses space a common resource of engine performance problems. After mile of service, vacuum hoses wear out, harden, split or soften; and vacuum tube deteriorates, turns brittle, and also breaks, resulting in all kinds of engine performance problems.

So at any time you an alert an engine performance problem and can't it seems to be ~ to uncover the source, include a vacuum leak diagnostic into your fix strategy.

Depending ~ above your certain vehicle make and also model, friend may discover various sensors and actuators that depend on a good vacuum resource to operate. For example, some engines usage a Manifold Absolute press (MAP) sensor that calls for vacuum come measure external air pressure.

A MAP sensor vacuum leak have the right to upset ignition timing and also engine stability and efficiency. A vacuum leak can likewise prevent one EGR valve from opening, cause engine overheating, and also increase harmful emissions. This form of leak deserve to also impact the positive Crankcase Ventilation (PCV) system.

Vacuum Leak Symptoms

Here is a list of performance difficulties to store in mind, as they can possibly be regarded a vacuum leak:

BackfiringHesitationHard startingLow engine powerPoor fuel economyPoor accelerationRough idleHigh idle or very low idle, depending on vehicle model.StallingStumblingCheck Engine irradiate onOxygen sensor reports a lean mixture continuously.Poor brake power (on vacuum-type power brakes)

Keep in mind the these symptoms space not exclusive come a vacuum leak. Because that example, a poor EGR valve, bad compression, or ignition timing problems may reason one or much more of these symptoms as well.

Vacuum Leak connected Trouble Codes

The following diagnostic trouble codes (DTCs) might be prompted by different species of faults, including a vacuum leak.

Trouble CodeDescription


Idle manage system malfunction


Cylinder details misfire


Fuel trim malfunction (bank 1)


System too lean (bank 1)


Fuel trim break down (bank 2)


System as well lean (bank 2)


II. Exactly how to discover a Vacuum Leak

OK. You have actually an engine power problem and also you want to execute some vacuum leak checking, where perform you start?

First, locate the vacuum chart for her vehicle. Girlfriend may uncover a copy that the vacuum chart on your vehicle owner's manual, however most auto manufacturers incorporate a diagram inside the engine compartment. Progressive the hood and look around the front of the engine compartment for a decal.

If friend can't discover one on your manual or in the engine compartment, you have the right to buy one at her dealer organization department. Another source is your vehicle repair manual. You deserve to buy an inexpensive aftermarket vehicle repair manual at your regional auto components store or online. The repair manual has actually all type of advantageous information your have the right to use because that maintaining and troubleshooting many automobile systems. So you'll do a an excellent investment.

The vacuum diagram shows the different vacuum controlled devices and also how they interconnect. Newer car models depict the contents resemblance and also their location.

OK. Now that you have the vacuum chart for her vehicle, you can start troubleshooting because that a potential vacuum leak. However, also if girlfriend don't have actually the diagram appropriate now, friend still deserve to follow the following steps.

(Note: If you are trying to discover a potential vacuum leak because of a trouble password you retrieved after ~ your inspect Engine Light come on, your automobile computer may be adjusting the air/fuel proportion to compensate; so the engine could not sound together if it had a power problem. If so, unplug the throttle place sensor or oxygen sensor, to pressure the computer system to operation the engine in "hard code" setting , so you can hear the engine rough idle. This will make it less complicated to detect the vacuum leak source during her diagnostic.)

If you suspect a particular an equipment (or several), you have the right to start through that device. Otherwise, monitor the diagram and start checking every hose. If friend don't have the diagram, examine each vacuum hose together you go around the engine. Many vacuum hoses are thin and soft, except for the one provided on the brake booster, i m sorry is more thickness and more sturdy in design, and also possibly the PCV hose.

Troubleshooting vacuum leaks calls for a close visual inspection the the hose, making sure it's correctly connected, and listening for the telltale hissing sound of the vacuum leak.

But noise from a running engine have the right to make it impossible to hear a hissing sound comes from leaky vacuum water tap or gasket. For this you have two options: You deserve to use a mechanic's stethoscope that helps come amplify the sound in your ear, or you have the right to use a size of hose because that the same purpose.

How to check Each Vacuum Hose

Follow the next actions to inspect each vacuum hose, maintaining a reasonable distance from moving components during her inspection:

Start the engine and let it idle. Set the transmission to Park (automatic) or Neutral (manual) and apply the emergency brake.Make sure the water tap is correctly connected, not loose or hanging free. It's straightforward to hit a hose loose inadvertently when doing maintain or replacing a component. You may need to use a small mirror and also a flashlight to check on hard-to-reach places, favor behind the intake manifold, throttle body, or exhaust manifold.Unplug and inspect both end of the hose. If the inside end of the hose is torn, worn, or widened, cut off the damaged component and plug the hose ago to the fitting.Trace the length of the hose with your finger to feel for rough, hardened, splitting, softened, or out-of-shape spots, especially approximately the hidden, underside of the hose. Also, try to feeling for vacuum at those turbulent or uneven spots.Check if the water tap is near or poignant a hot surface.Also, inspect hose connectors, tees, and also unions for cracks and also looseness. Change them as necessary.Pay unique attention to the check valve the connects the brake booster to its vacuum hose. If leaking, you may hear a hissing sound.Check the water tap for contamination as well, prefer oil, coolant, or some various other substance. Disconnect the water tap from the maker it associate to and check within the device connector. If you discover a foreign substance inside the hose, contamination has potentially reached inside the an equipment as well, more than likely not work properly. You might need to check the device for appropriate operation.As component of her visual inspection, incorporate the gadgets the vacuum hoses attach to. Check the tools for damage like cracks, dents, and loosened parts. These may develop a vacuum leak as well. Pinch the vacuum line resulting in the device, and also spray soapy water ~ above it and also hear because that a adjust in idle speed.If you uncover a hose with a softened, hardened, or damaged spot, change it.

You can likewise spray water ~ above a hose, ports and connectors to assist you examine for leaks.

Using a Vacuum Gauge

You can also use a vacuum gauge to more confirm the presence of a vacuum leak, if necessary. If friend don't very own a gauge or don't want to purchase one appropriate now, your neighborhood auto components store might loan you one.

Follow the instructions that come with the tool and the tips had in the article linked above.

Pay distinct attention to needle movement patterns. A stable low or really low reading may suggest to a gasket (intake or throttle) leak, amongst other potential faults.


III. Check the entry Manifold because that Vacuum Leaks

Although you're more likely to conference a vacuum hose leak, intake manifold gasket leaks additionally happen. If your previous check didn't revolve out anything wrong, check the entry gasket in between the manifold and cylinder head, and the basic gasket located between the entry manifold and throttle human body or carburetor.

To inspect these gaskets you deserve to use among two basic alternative methods:

Soapy water in a spray bottle.A size of hose (or mechanic's stethoscope).

Any among these methods is good.

Apply the emergency brakes.Set your transmission to Park (automatic) or Neutral (manual).Block the wheels to it is in safer and prevent the car from moving.Start the engine and also let it idle.To usage the soapy water, spray a tiny around the intake manifold whereby it mates through the cylinder head and around the base of the carburetor or accelerator body. Don't forget to visually check the entry manifold itself for cracks and spray water on suspect spots.Listen for any kind of changes in the engine idle.If the engine smooths out as you spray water, you've discovered the vacuum leak; girlfriend may also see bubbles on the ar of the vacuum leak.

Note: To use a hose (or mechanic's stethoscope), ar one finish of the hose against your ear and move the other end of the hose approximately the leaf of the intake manifold gasket and also carburetor or throttle body gasket. If there's a leak, you'll hear a hissing sound.

If you found a vacuum leak one of two people at the intake manifold or in ~ the basic of the accelerator body, very first try tightening the entry or accelerator body mounting bolt:

Tighten the bolts gradually, adhering to a crisscross pattern—when tightening a manifold, begin at the center and also work your way out.Tighten the bolts come the torque detailed in your auto repair manual using a speak wrench.Check again for the vacuum leak.If the leak is tho present, you'll should replace the intake manifold gasket or throttle body gasket.Follow the accuse in your car repair hand-operated to change either gasket.

Watch the video clip below see just how the male uses water come diagnose a misfire top top cylinder one.

IV. Utilizing a Hand Vacuum Pump to Test devices for Vacuum Leaks

Often, a cautious visual and also manual inspection like the one described above is sufficient to discover a vacuum leak. Yet not every the time.

Some materials that run with vacuum might suffer internal damage (a diaphragm might rupture, for example). And also you can't diagnose this type of damage by touch or sight.

So, if you doubt a vacuum leak however can uncover the source, this is the following step in her troubleshooting strategy.

For this, you'll should use a hand-operated vacuum pump. You might buy one at most auto parts stores or online. The vacuum pump helps in troubleshooting emission systems. But if girlfriend don't desire to buy the tool appropriate now, your neighborhood auto components store may loan you one.

Follow the instructions that come through the vacuum pump for procedure instructions and also the repair hand-operated for your particular vehicle for the measures in troubleshooting the maker you should test.

Some time you should troubleshoot a device under particular operating conditions, or in conjunction with one more tool. Although this kind of troubleshooting might sound complicated, you don't need special training. You execute still need to follow the device operating instructions, however, and also the repair hands-on troubleshooting steps.

Also, follow these tips when using a vacuum pump:

Make certain the connection in between the pump and also the maker is tight—use the exactly diameter connector or water tap to make the connection.Only use the appropriate amount that vacuum for the maker you are trial and error (usually 10 come 15 in Hg; consult her repair manual).The fewer connectors, adapters, and also hoses you usage to connect your hand pump come the machine you want to test, the better.


V. Vacuum water tap Repair Tips

Dealing v damaged vacuum hoses doesn't necessarily median you should replace them. Often, a vacuum hose just requires a simple repair that can take you a pair of minutes or so.

You can repair a damaged vacuum hose finish in a minute. Many of the time you can gain away through cutting off about half an customs at the end and also reconnecting the hose.Be cautious when dealing with damages located between the ends of a vacuum hose. If you simply need to fix a little hole less than fifty percent an inch, cut out the damaged area and use a union come reconnect the two pieces back.Repair one vacuum water tap at a time to protect against confusion. Part vehicles, specially oriental brands, come with numerous vacuum hoses that can make it confusing to repair when they interconnect in miscellaneous ways. Because that these cases, you can find 1-, 2-, 3-, 4-way, and also elbow connectors to deal with almost any kind of hose routing and repair.Always label hoses and also their corresponding connectors or fittings, so that you reinstall repaired or brand-new hoses to their matching fittings.If you find one or more disconnected hoses, use your vacuum diagram to reconnect the water tap to the exactly fitting.After making a repair, route and secure the vacuum hose far from warm surfaces and moving components.Always replace a vacuum hose with one of the exact same diameter and also length, and also for the application intended (PCV, brake booster, or consistent vacuum).

This content is accurate and true come the ideal of the author’s knowledge and is not meant to substitute for formal and also individualized advice native a default professional.

Questions & Answers

Question: My inspect engine light come on, and I went to the mechanic who stated it to be a P0171 error. Financial institution 1 device 2 lead as well lean. I cleaned the massive air circulation sensor and all was fine for approximately 800 miles and two weeks. However, it returned with the very same code. Ns pulled out the MAF sensor to view if it was dirty and also it looked fine. What is my following step?

Answer: This other article may help:


Question: when fixing a vacuum leak, just how long after ~ resetting the p071 code will certainly it revert if not fixed?

Answer: In general, if friend are taking care of an intermittent problem, it might take a while for the irradiate to come earlier on, till the part fails again and also the computer detects the problem. If there's a failed, monitored part, it more than likely will take it a couple of hours for the computer to detect that again.

Question: What could my difficulty be? mine 2001 Chevy Blazer has consistent air sound. Noise is within the cabin and rises in ~ idle only while rest is pressed. No liquid loss yet with the ignition off, ns pump the brakes, castle don't get harder, and also yet castle sink if held while starting, feeling spongy and pedal practically sink come the floor. Just start to learn around diagnosing for a vacuum leak. I will inspect the hoses tomorrow. And also your aid would be greatly appreciated. Any ideas?

Answer: that sounds favor you may have actually a vacuum leak in the brake booster. This other write-up may assist you diagnose the problem:


Question: What space the most usual vacuum leaks ~ above the manifold?

Answer: inspect vacuum hoses condition and connectors. Then examine for input gasket leaks. Sometimes spraying part carburetor cleaner on doubt leaks help to uncover damaged hoses and leaks.

Question: If i disconnect a vacuum hose and also hear a hissing sound, go that show that mine vacuum is good? Meaning, if over there is a leak, over there wouldn’t be a suitable seal to save that pressure/vacuum on the line and also no hiss would certainly emit as soon as the line is disconnected.

Answer: that is hard to discover a little leak just by disconnecting a vacuum hose. You'd think the hose and also fitting space perfectly good. A vacuum might leak v damaged hoses, gaskets, and faulty valves. If you are suspecting a leak, shot using a vacuum gauge. It'll be an ext accurate. This other short article may help:


Question: I'm restoring a 50-year old Jeepster 258-6. I have actually replaced the input manifold gasket and put top top headers. My jeep beginning up yet within 3 seconds, the RPM sounds choose it shoots increase to about 2500 and also dies. Could it be the gasket? The jeep will only run because that 3 seconds.

Answer: it seems prefer a large vacuum leak. It might be the entry manifold or basic carburetor gasket. Your regional auto components store may loan friend a exhilaration machine. Hook it up to the brake booster hose. Expect this helps.

Question: how do you solve an wait leak top top a crate stock go-kart motor?

Answer: inspect the gaskets; the one in between the carburetor and also air box could be leaking.

© 2016 Dan Ferrell


Dan Ferrell (author) on June 25, 2020:

Make certain all the vacuum hoses are appropriately connected, and in an excellent condition. Examine for intake gasket leaks. Make sure the MAF sensor is working fine, and also check ignition timing. You may need your vehicle repair manual for few of this checks. Expect this helps.

Frances hernandez ~ above June 25, 2020:

2005 Chevy Impala go the head gaskets when put in equipment it backfires won't move

Dan Ferrell (author) top top June 09, 2020:

This video might offer you one idea how to attach the hose:


Serena ledsome on June 09, 2020:

I have a 99 vw jetta v 2.0 ns trying to attach crankcase breather hose

Dan Ferrell (author) on might 19, 2020:

Nice tip.

hardlymoving native Memphis, TN on may 19, 2020:

Easy method to uncover a vacuum leak is come spray fog approximately the vacuum lines and also air intake areas with a brake clean aerosol spray. If the engine rpm's climb after spraying the brake clean top top or around the water tap or entry component, you've uncovered your leak.

Dan Ferrell (author) ~ above October 23, 2019:

Vacuum hoses periodically collapse after mile of service. A flatten vacuum hose will restrict flow. Check the other hoses as well and also replace them together needed.

James top top October 23, 2019:

I have actually a 2010 GMC Terrain literate 140K. Stormy idle; discovered a fell down hose/line leading from the accelerator body to a connection near the fire wall. Should this water tap be flat?

Dan Ferrell (author) ~ above September 30, 2019:

A faulty throttel positon sensor and fuel pump can show this kind of symptoms. Although no as common, a fuel pump relay have the right to behave badly as well. A crankshaft place sensor, or any other sensor v a coil for the matter, may reason this problem as well. But this normally is a temperature connected issue. You have the right to drive for a couple of minutes until the component's temperature rises and the (broken) coil opens and the automobile stalls. Faulty ignition coils may behave like this together well.

This other article can offer you some details on this problem:


Hope this helps.

Nick Germinario on September 30, 2019:

My 94 corvette started stalling while driving. A mechanic told me he think it the optispark distributer. He stated the is no spark after that stalls. I think it's the coil failing once the engine gets hot. Require help

Dan Ferrell (author) on might 04, 2019:

Vacuum leaks can be difficult to locate. Occasionally a smoke machine diagnostic deserve to be of an excellent help. If the check engine irradiate keeps coming on, one emissions test may help. View what space the emissions that space increasing and also trace earlier the feasible sensors or contents behind the source.

Donna Galyan on might 04, 2019:

I have actually a 2005 Ford emphasis that is giving even the mechanics a head ache. I constantly is giving us a to run to skinny on financial institution 1 code. I had actually a mechanic operation a computer to discover the trouble yesterday. All components are to run properly. All he can find is one small vacuum leak. He cleared the code. I let the vehicle idle because that a hour. No light. Turned turn off the car. Later on started the engine and drove it out of the parking lot and the light came on. I changed the computer 02 sensors tune up. What doesn’t make sense is the vehicle runs great. Any ideas. This one is stumping mechanics with forty year of experience. Thank you

Dan Ferrell (author) top top January 26, 2019:

Even without stalling, the speak converter can cause some problems. Shot this: press the brake pedal contempt to engage the brake switch and begin come accelerate. See if you an alert any difference. In which instance there might be a difficulty with the clutch or the computer system itself. A clogged injector is also a great possibility and additionally check the throttle place sensor. Expect it helps.

Jeff ~ above January 25, 2019:

Thanks for reply Dan. Infection does not change gears, increase or down throughout this. And it is every trip. No matter what ground speed or engine speed nor what equipment the trans happens to it is in in, it is constantly there. The only time anything changes about it is if i am under a slight load, going up a hill while roughly 30-45mph which placed s the engine around 1350-1500 rpms. There is no bucking like a fouling spark plug or wire would reason in older engines. The is a an extremely subtle point for the many part, you deserve to just hear that constantly rise up and also down every 1-2 seconds. No stalling the some other Jeep owner speaking the ‘surge’ that finish up recognize the trans no locking increase properly. As soon as going under from rate for a irradiate or prevent sign, no issue the rate of de-acceleration, do not have and also tendencies of a stall like they describe. Fuel trims phone call me that is make the efforts to run rich through controls cutting it earlier and ltft’s reflecting -1.3 come -3.9, and stft’s bouncing native zero come -3.9 while in ~ idle. ? Vacuum leak or injectors? Can’t seem come find any type of leaks, execute not hear any hissing. I have actually 85,000 mile on the now. A bit early on for plugs and also pcv, but because I am close to the 100,000 note I’m walk to change them out anyway.

Even as soon as it is at its worst, there is no bucking or jumping, however at those moments you carry out feel the slow and speeding up of the Jeep, yet again, subtle like.

Dan Ferrell (author) top top January 25, 2019:

That is a pesky problem to diagnose. Ns was thinking a feasible extreme skinny fuel injection. The O2 sensor appears within range, however the short and long hatchet numbers are something else. The ECU may be trying to compensate, and it might be being successful at it (according come the ECU) since there space no DTCs yet. However this other write-up may provide you some concepts on this that might help.


An ignition system problem could be one more possibility.

Do you feeling the transmission suddenly changing gears? This may suggest a problem with an electronically managed transmission module.

Also, one intermittent electrical trouble affecting engine or drivetrain systems.

I great I might be more specific. Hope any of this helps.

Jeff ~ above January 25, 2019:

I have a 2014 Jeep Wrangler w/3.6l Pentastar that is driving me crazy. At begin up and also at cold or hot idle, all seems ok. Driving, at any speed or equipment (Auto tans) over there is a surging or pulsing in engine RPM’s. For most part, that is very subtle, tach doesn’t even register it, but you can absolutely hear it. Put in slight load, little hill about 30-45mph range and the becomes really evident, tach it is registered a 50rpm or therefore swing, return by ear you deserve to tell it is huge than that, would certainly guesstimate as 100-150rpm. I have looked for vacuum leaks, adjusted Crankshaft place sensor, checked MAP sensor and also AIT sensor. My small FlashCal shows the O2 sensors in intended range, but at idle, short and long hatchet fuel trims are negative numbers choose it is being over fueled. I have actually not looked in ~ them while driving, safety first.

It does not seem come be transmission related, together it is any speed, any type of gear or rpm. TPS in my mind is ruled out as well as they would commonly be a position selection issue. ?

Throttle human body is pulled and also cleaned every 15k miles with brand-new gasket/seal, every seems an excellent there.

Any idea whereby to look? too it to two shops, both agree over there is a problem but with no fault codes ever before being thrown, say keep driving, the will eventually throw a password to aid narrow it down. 18,000 mile later worry has no gotten far better nor worse but has yet to throw a code.

Dan Ferrell (author) on January 07, 2019:

It sounds an ext like one idle regulate (IAC) actuator or ignition system, sticking EGR valve problem. There might be other reasons. Girlfriend still have to diagnose the difficulty to inspect where it's comes from. Check for feasible trouble codes.

gone2long top top September 05, 2018:

Great stuff, give thanks to you. Expect to obtain a an answer to my related question. Best, G2L

Dan Ferrell (author) on June 11, 2018:

Hi Emmyboy,

Vacuum leaks are tough to find sometimes, yet you acquired to be patient. Check every hose and also connection first, then examine the gaskets and also under the accelerator body.

Good luck

Emmyboy from Nigeria ~ above June 11, 2018:

Nice information.

Thanks because that sharing.

See more: Felony Friendly Housing Portland, Oregon That Is Willing To Work With A Felon

Wish I might just get an experienced who will resolve this destructive engine vacuum leak problem that ns am experiencing at the moment.