# Finding vacuum leaks. Best way?



## Black_cabbie (Jul 16, 2003)

Somebody told me to use a lighter. Just push the button and start moving it near suspected areas.... Are we looking to a cabriolet fireball here?


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## kamzcab86 (Feb 14, 2002)

*Re: Finding vacuum leaks. Best way? (Black_cabbie)*

Can of carb cleaner is what I often hear http://****************.com/smile/emthup.gif


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## bLac K aBriOleT89 (Jun 18, 2004)

*Re: Finding vacuum leaks. Best way? (kamzcab86)*

yeah..me too, look for bubbles or changes in iddle speed!


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## Black_cabbie (Jul 16, 2003)

*Re: Finding vacuum leaks. Best way? (bLac K aBriOleT89)*


_Quote, originally posted by *bLac K aBriOleT89* »_yeah..me too, look for bubbles or changes in iddle speed!

I tried it and it cleaned the area I was spraying. Then I had to clean the rest of the engine to make it look good. 
Btw, Lighters have butane in them right? 
People mention propane as well...


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## mgyver74 (Dec 10, 2003)

*Re: Finding vacuum leaks. Best way? (Black_cabbie)*

As long as U aren't holding fire to the engine I don't see what would be so bad.(Yes it's flammable..but so is carb cleaner)...But since you cant see the gas from a lighter how are U going to see the leaks? 
I am not a fan of using propane for anything except barbecue fuel or as an alternative fuel since it has a tendancy to go boom...








Of course when I was younger (and stupider) I once charged an AC system with propane cause I couldn't afford the R12....Strangely enough, it worked...


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## Black_cabbie (Jul 16, 2003)

*Re: Finding vacuum leaks. Best way? (mgyver74)*

I am going to try it tonight and see what happens. One candidate is the idle screw because when I push it or move it arround the idle changes but not the rpm. I am 100% sure it leaks from there too.


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## bLac K aBriOleT89 (Jun 18, 2004)

*Re: Finding vacuum leaks. Best way? (Black_cabbie)*

My lighter just says _"KEEP AWAY FROM CHILDREN_"


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## chef.stephen (Feb 15, 2005)

*Re: Finding vacuum leaks. Best way? (kamzcab86)*

A can of starter fluid.
Spray it on any junctions or suspected leaks. If the idle speed increases you have a leak, simple.
You probably won't see bubbles because the vacum lines are sucking air in not blowing out.


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## meinit (Jan 26, 2004)

*Re: Finding vacuum leaks. Best way? (Black_cabbie)*


_Quote, originally posted by *Black_cabbie* »_Somebody told me to use a lighter. Just push the button and start moving it near suspected areas.... Are we looking to a cabriolet fireball here? 

How to: Fix Vacuum Leaks 
VWs are not generally cursed with the spaghetti of vacuum lines found under the hoods of many other cars. Nevertheless, vacuum lines are used in VWs and can cause trouble from time to time - creating the so-called "false" air syndrome. 
Air entering the engine that is unmeasured by the fuel injection system's air flow sensor is known as "false" air and will tend to lean out the engine's carefully controlled air-fuel ratio. Symptoms may include hesitation, bucking, poor throttle response, surging at small throttle openings and power loss. Serious vacuum leaks will play havoc with driveability as well as the operation of vacuum operated devices including power brakes, air conditioning vent flaps and power locks. A vacuum leak can occur anywhere there is a joint or fitting that connects directly to the intake air flow, along the length of any plastic or rubber vacuum hose, around a worn-out valve cover gasket or around the fuel injector seals. Especially look for hoses that may have chafed through from continually rubbing on something. 
Air Flow Sensor 
Start your hunt for vacuum leaks at the Digifant air flow sensor/air filter housing. Check the rubber duct between the air flow sensor and the throttle body for signs of splits or cracking. Cracks in the duct may only open up under acceleration when the engine torques rearward in its mounts. Remove the duct and inspect it carefully, twisting it in your hands (remember your gloves) while you look for cracks or splits. Reinstall the duct, making sure it seats correctly on the air flow sensor and the throttle body and that the hose clamps are not cocked or pinching the rubber when you snug them down. A light smear of clean oil on the metal mating surfaces can ease the installation of the duct. 
Temperature Regulator Valve 
The temperature regulator (or preheat) valve is located in the air flow sensor box above the air filter. The regulator valve's purpose is to control the operation of a flap in the air box which diverts heated air from around the exhaust manifold to the intake during starting in cold ambient temperatures. The regulator valve has two vacuum fittings which protrude through the side of the air box. A short vacuum line of white plastic runs from the lower fitting on the box to the diaphragm which controls the intake preheat valve. A longer vacuum supply hose runs from the upper fitting on the box to the throttle valve. A tee in this hose splits off to the fuel pressure regulator which is located at the right (passenger) end of the fuel rail. Check all of these lines for chafing, holes and snug connections. 
PCV Valve 
The positive crankcase ventilation valve (PCV) is another potential source of vacuum leaks. The PCV sits on the valve cover. The crankcase ventilation hose which connects to the PCV should be clean and free of cracks or splits. Follow the hose to where it connects to the throttle valve and make sure the connection is tight. The hose clamps should be in good condition and properly snugged down, but not so tight that they bite or cut into the rubber. Check the rubber grommet in the valve cover where the PCV mounts for a snug fit. The grommet should be free of cracks or other visible injury. See below for instructions on cleaning the PCV valve. 
Power Brake Booster 
With your engine off, step on the brake pedal eight or ten times to let air into the power brake vacuum booster. Now, hold down the brake pedal and start the engine. The pedal should drop slightly as vacuum builds in the brake booster. Vacuum leaks in the brake booster are exceedingly rare. Suspect other sources first. 
Other Potential Vacuum Leaks 
Evaporative Emissions Control Canister 
Air Conditioning 
Vacuum powered door locks 
Dipstick


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## chef.stephen (Feb 15, 2005)

*Re: Finding vacuum leaks. Best way? (meinit)*









Impressive: http://****************.com/smile/emthup.gif


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## kamzcab86 (Feb 14, 2002)

*Re: Finding vacuum leaks. Best way? (chef.stephen)*


_Quote, originally posted by *chef.stephen* »_








Impressive: http://****************.com/smile/emthup.gif









Meinit, that belongs in the FAQ! http://****************.com/smile/emthup.gif


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## VeeDubDriver1990 (Jul 19, 2004)

*Re: Finding vacuum leaks. Best way? (mgyver74)*


_Quote, originally posted by *mgyver74* »_As long as U aren't holding fire to the engine I don't see what would be so bad.(Yes it's flammable..but so is carb cleaner)...But since you cant see the gas from a lighter how are U going to see the leaks? 


Interesting story with that starting fluid- trying to get a Chevy Baretta
to start one day at work, someone sat inside the car and I sprayed
the fluid through the plastic air tube directly into the throttle body and
a HUGE fireball came up to greet me














The car started,
though








I think I was set-up








Detecting vacuum leaks? I would say "soapy water solution", but that
could get into the system and mess everything up real good








Why not just replace all the hoses? Fairly inexpensive, I reckon








That's something I should practice myself, but I always forget about it


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## tolusina (Oct 19, 2004)

*Re: Finding vacuum leaks. Best way? (Black_cabbie)*

The absolute BEST way?? 
Right here, http://www.otctools.com/newcat...d=315 or similar.


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## BigDaddyJimmyJam (Jan 31, 2005)

*Re: Finding vacuum leaks. Best way? (tolusina)*

How To Fix Vaccum Leaks:
1. Replace all Vaccum Lines.
2. Crack open a beer and say "damn, sure does beat all the what ifs"


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## kamzcab86 (Feb 14, 2002)

*Re: Finding vacuum leaks. Best way? (BigDaddyJimmyJam)*


_Quote, originally posted by *BigDaddyJimmyJam* »_How To Fix Vaccum Leaks:
1. Replace all Vaccum Lines.
2. Crack open a beer and say "damn, sure does beat all the what ifs"









http://****************.com/smile/emthup.gif


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## Thomas_covenant (Oct 27, 2004)

*Re: Finding vacuum leaks. Best way? (meinit)*


_Quote, originally posted by *meinit* »_
How to: Fix Vacuum Leaks 
VWs are not generally cursed with the spaghetti of vacuum lines found under the hoods of many other cars. Nevertheless, vacuum lines are used in VWs and can cause trouble from time to time - creating the so-called "false" air syndrome. 


Looks like that one's for Digi cars. Here's a write-up I did for CIS cars:
You can use a dwell meter on the Lamda Test port to help check for and find vacuum leaks. Ideally you should have the fuel mix set correctly when you *know* that there are no leaks. Any leak that occurs will lean out the mixture, causing an increase in the dwell reading at the Lambda Test Port.
So the place to start is to verify what the Lambda actually is set to when there are no leaks. Here's what I did with "Evil Otto", the 1981 cabbie when I first got him. Parts you'll need are ziplock freezer bags and a can of starter fluid. Tools: Flathead and phillips for the hose clamps, a pencil or golf tee (for plugging lines) and a dwell meter.
1. On the intake manifold are 2 large nipples. One connects to the brake booster (and has 1 or 2 smaller nipples on the check valve that feed vacuum to the reservoir and under-dash and to the vacuum retard if you have that), the other connects to the valve cover. Remove the hoses from the 2 nipples. Take thick plastic (I use zip-lock freezer bags as they are tough and temperature resistant) and put it over the nipples. Then put the hoses over the plastic and clamp them tightly.
2. On the back side of the manifold, pass side, is a thick hose leading to the Aux Air Regulator. Remove the hose from the Aux Air Regulator side and put plastic over the Aux Air Regulator nipple. Put the hose over the plastic and clamp it.
3. On the throttle body, locate the nipple sticking out on the back. Put some plastic on that (may have to use thinner plastic) and clamp the hose on the plastic.
Now all the auxiliary stuff is disconnected and you can start checking the basics. Hook up the dwell meter to the lambda port and start the engine. Remember, you do *not* have power assist to your brakes at this point, so do not drive! If your O2 thermo sensor (also called "Lambda temp sensor") is working, the dwell should read around 70 degrees or so for a couple of minutes. This is called "Cold Enrichment". If the dwell doesn't hit around 70 and stay stable then either your O2 thermo sensor is faulty, or it's warm enough outside to keep this from turning on. It's supposed to turn off at around 77 degrees F.
Once the car warms up a bit (doesn't take much) the switch will open (if it wasn't already) and the dwell will shift and start to oscillate a bit. Usually swings 10 degrees or so. Don't worry if the reading seems really low, that's because we don't have the PCV system hooked up, so it is actually running a bit richer than normal. Do not adjust the fuel mixture at this time!
Once the dwell meter is swinging (indicating operation of the O2 sensor), take your starter fluid and, using the straw proceed to spray the following points:
1. Main intake system - Spray at the boot over the air flow plate, then where the boot connects to the hard plastic, then where the plastic connects to the bellows leading to the TB, then where the bellows meets the TB.
2. Fuel injector orings - spray at the base of each fuel injector. Be sure to spray right at the base of the injector, and not on the backside of the head where the intake manifold meets.
3. Intake manifold gasket - Look past the fuel injectors and you'll see the gasket where the manifold meets the head. Spray each of the intake tubes right where the tube meets the head.
4. Aux Air Regulator hose - spray all along the Aux Air Regulator hose, especially where it meets the manifold and the Regulator.
5. Idle screw - work the straw around the back and liberally spray the head of the idle screw.
6. Cold start valve - spray all around the cold start valve where it meets the manifold.
7. TB gasket - spray all around where the TB meets the manifold to test the TB gasket.
While spraying each point, watch the dwell meter. If you spray where there is a leak, the dwell meter will dip down for a few seconds because you have riched out the mixture a bit. The engine may surge or stumble as well.
Now you have a comprehensive list of the leaks on the basic engine, without all the Aux stuff. Fix the leaks. On Evil Otto I had to change the intake gasket, FI orings *and* seats (2 cracked seats), and the TB gasket.
Once you have all these leaks fixed you can move on to testing the rest of the system.
First, locate the tube that connects the valve cover to the intake manifold. Remove the tube, take out your piece of plastic and put the tube back on. Be sure to clamp it tight. Next, look on your pass side strut tower. If you have one or two black boxes there (idle boost valves) then you will see the bottom tube goes to the intake manifold. Disconnect this tube and put your plastic on, then put the tube on the plastic and clamp it down. All we've done here is add in the PCV system. The PCV system draws air from above the air filter, through a pipe to the intake manifold, pulling clean air into the engine. This air circulates in the engine to pick up blowby gases and is then pulled into the intake manifold.
Start the engine and watch the dwell meter. It should be 10 degrees or more higher than it was last time, and bouncing about 10 degrees up and down (i.e. bouncing from 40-50, centered on 45 is ideal). Don't worry too much if it's higher or lower than this, as you may have a PCV system leak. Leak check the PCV/Engine first, then we'll set the fuel mixture.
Leak checking the PCV system is simple. Take your starter fluid and spray all around the dipstick while watching the dwell meter. If the dwell meter reading drops, then the dipstick funnel or the dipstick stop (plastic piece on the dipstick itself) is leaking and needs replacement. Next spray around the oil filler cap. Again if the dwell reading drops, the cap is leaking. Next spray all around the valve cover where it meets the head to test the valve cover gasket. If you find leaks, you'll have to fix them.
Once you've verified the PCV system is leak free, then you can pay attention to the dwell reading vis-a-vis having a correct mixture. The dwell meter should be reading 45 ideally, meaning that it bounces between 40 and 50. If it's up to 5 degrees higher or lower, then it's still well within the system's ability to compensate and no adjustment is needed. If it's higher than 50 or lower than 40 you should adjust the mixture.
At this point you have successfully hunted and fixed all the vacuum leaks in the main system. You're nearly done!
If you have the idle boost valve(s), remove the electrical connector(s) from them and pull the tube at the valve cover, pull off your plastic and put the tube back on. Start the car. The dwell should not read higher than it did in the last test. If it does, then the tube from the idle boost valve(s) is leaking, or the boost valve is leaking. Testing is listed in the Bentley and Haynes...it's beyond the scope of this write-up. Fix it.
Next step is to pull the tube from the brake booster and remove the plastic, then put the tube back on. Clamp it well. Locate the small nipples on the check valves and remove any tubes from them. If you have one nipple, plug it (vacuum line with a pencil stuck in the other end). If you have 2 nipples, connect them together with a vacuum line. Start the car. The dwell should not be higher than it was in the last step. If it is, then you have a leak in the booster line or booster. Again, bentley or haynes can help with t/shoot and repair.
The next step is to connect up the vacuum lines that go to the small nipples on the Brake Booster Check Valve. You'll want to do this one at a time. Just for the sake of knowledge, the following lines should connect to the brake booster check valve nipples:
1. Vacuum line to retard side of the disty bubble (if you have the two-pipe bubble, newer cars do not).
2. Vacuum line to the under-dash HVAC (if car has AC). This should first go to a small check valve, then it splits. One side goes to the vacuum reservoir (egg crate) and the other side goes to the rain tray on the pass side, then to the under-dash.
To test this, first connect ONLY the retard line to the brake booster check valve nipple, keeping the other nipple secured. Start the car. You'll notice the idle has dropped, this is because the timing is being retarded. It's normal. If the idle didn't drop, you've got a problem. Look at the dwell gauge. If the dwell has increased, then you've got a leak. Pull the line at the disty vacuum bubble and put your thumb over it (or a pencil in the end). If the dwell now drops to normal, then the vacuum bubble is leaking internally. If the dwell is still high, the line is leaking somewhere.
Last is the under-dash/reservoir. First, connect the line from the check-valve to the brake booster check valve nipple. Then disconnect the line leading to the tee and set it aside. Put your thumb over the nipple on the check valve (or a short piece of vacuum line with a pencil stuck in the end). 
Remove the line from the reservoir to the tee and connect it to the check valve. Start the car. If the dwell is higher than in the previous step, then the check valve or the tube to the nipple is leaking. Starter fluid will help you determine which. Fix it.
Next remove the line coming from the reservoir to the tee. Connect this line directly to the check valve. Start the car. If the dwell reads higher, the line or reservoir is leaking. Use the starter fluid to find the leak, paying special attention to the grommet where the tube enters the reservoir.
Next, remove the reservoir line from the check valve. Connect the line from the under-dash to the check valve. Start the car. If the dwell is higher then you have a leak in the line or in the under-dash. If you are unable to repair this leak at this time, you can turn the check valve around to prevent it from causing a vacuum leak to the engine. Once you've fixed the leak you can put the check valve back the correct way.
That's it! Once you've repaired all the leaks and have the fuel mixture adjusted you can have a beer or whatever and be happy knowing that your car is happy.
In addition, because you have the mixture adjusted correctly when you *know* there are no leaks, in the future if the engine isn't quite right, warm it up and use the dwell meter. If the dwell reads higher than what you had it set at, you'll know that you have a new leak and your trusty can of starter fluid will serve you well!
As always, this was written by a relative amateur and may have errors. It is what I did on my car and it worked, so I wrote it up. If you have suggestions, corrections, additions, subtractions, etc please feel free to IM me or email me and let me know!!! All comments are welcome!
Thomas


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## kamzcab86 (Feb 14, 2002)

*Re: Finding vacuum leaks. Best way? (Thomas_covenant)*

http://****************.com/smile/emthup.gif Nice write-up Thomas
(This thread has now been added to the FAQs







)


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## ensone (May 18, 2004)

*Re: Finding vacuum leaks. Best way? (kamzcab86)*

dont spray carb cleaner by the coil


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## Black_cabbie (Jul 16, 2003)

*Re: Finding vacuum leaks. Best way? (ensone)*


_Quote, originally posted by *ensone* »_dont spray carb cleaner by the coil









I want to know how you found out.........


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## briano1234 (Feb 20, 2004)

*Re: Finding vacuum leaks. Best way? (Black_cabbie)*

in the words of Johhny reed FLAME ON


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## Moljinar (Sep 20, 2001)

*Re: Finding vacuum leaks. Best way? (briano1234)*

Use Gumout Carb cleaner. It's not flamable! Makes idel drop when a leak is discovered.


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## ensone (May 18, 2004)

*Re: Finding vacuum leaks. Best way? (briano1234)*

i forget who told me not to spray the coil... im pretty sure it was chris (vtgti) i think he mentioned something about him having a little 2 much fun before the fireball








chris helped me find my leak.. turns out it was the connection to the afm


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## Moljinar (Sep 20, 2001)

*Re: Finding vacuum leaks. Best way? (tolusina)*


_Quote, originally posted by *tolusina* »_The absolute BEST way?? 
Right here, http://www.otctools.com/newcat...d=315 or similar.

Couldn't you just stick a burning rag in the intake and do the same test?


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## 97VWcabrio (Oct 3, 2005)

*Re: Finding vacuum leaks. Best way? (Black_cabbie)*

I didn't read through any of the long posts, so sorry if i am repeating anything that was said. 
1) You can light a cigarette and move it around near vacuum lines. When you see the smoke getting pulled in, you found your leak. 
2) You can buy a miti-vac, or equivatent. It's a hand operated pump, you squeeze it and it creates a vaccuum. you can take the intake tube off at the throttle body and stick an air hose in there, make sure it's sealed up real well with something air tight, like ducttape or something, and pump away...listen for air leaks.
This way is easier in my opinion than trying to find the leaks with the car on, because you don't have to struggle to hear the vaccuum leak over the engine. 
3) same concept as #2 except you use a vaccuum source that works on compressed air.....this is what i do, i hook the vaccuum pumps up to the compressed air, and leave it somewhere far away, like in the house, and then i run a line out to the car, and stick it in the throttle body. This again is to eliminate backround noise to make the leaks easier to hear. 
Hope this helps


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## charlesk (Sep 17, 2005)

*Re: Finding vacuum leaks. Best way? (97VWcabrio)*

cigerette trick worked for me many times over the years to find vacum leaks it sucks it in to find a air leaks it blows the smoke around


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## briano1234 (Feb 20, 2004)

*Re: Finding vacuum leaks. Best way? (charlesk)*

I refuse to let my cabby start smoking.....


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## nsmsam (Feb 5, 2003)

*Re: Finding vacuum leaks. Best way? (chef.stephen)*


_Quote, originally posted by *chef.stephen* »_A can of starter fluid.
Spray it on any junctions or suspected leaks. If the idle speed increases you have a leak, simple.
You probably won't see bubbles because the vacum lines are sucking air in not blowing out.

Does starter fluid come in a spray can? or we put that into spray bottle ourself ?


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## kamzcab86 (Feb 14, 2002)

*Re: Finding vacuum leaks. Best way? (nsmsam)*


_Quote, originally posted by *nsmsam* »_
Does starter fluid come in a spray can?

Yes.


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## Black_cabbie (Jul 16, 2003)

*Re: Finding vacuum leaks. Best way? (kamzcab86)*

wow, a 2 year thread bumped.....


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## olds442 (Jun 7, 2004)

*Re: Finding vacuum leaks. Best way? (Black_cabbie)*

If it is CIS - you might as well start replacing hose connections, injector seals, and idle by pass screw seal. It is likely that one of them is the culprit and if not now, they will be in the near future. I think you can get all the stuff to complete this for less that $30.
Then put a dwell meter on the test port and adjust the idle mixture and you will be a happy camper.


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## pj42 (Aug 5, 2012)

*2002 Jetta BDF loses vacuum when AC is on*

Meinit, 

You list the AC system as a possibility for a vacuum leak. The car I'm working on has normal vacuum with AC off (20" steady at idle, recovers quickly from snap test). But as soon as the AC is turned on it drops to 17" and then varies, sometimes drops as low as 13". It gets worse every time the fans come on, I believe the compressor is actuated every time the fans come on as well. 

I think I can hear the vacuum leak from near/inside the blower box but I can't figure out why there might be vacuum lines going in there since the air doors appear to be motor controlled. 

What is exactly the relation between the vacuum system and the AC system? 

PJ 






meinit said:


> _Quote, originally posted by *Black_cabbie* »_Somebody told me to use a lighter. Just push the button and start moving it near suspected areas.... Are we looking to a cabriolet fireball here?
> 
> How to: Fix Vacuum Leaks
> VWs are not generally cursed with the spaghetti of vacuum lines found under the hoods of many other cars. Nevertheless, vacuum lines are used in VWs and can cause trouble from time to time - creating the so-called "false" air syndrome.
> ...


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## briano1234 (Feb 20, 2004)

Which model year are you talking about? 

As I under stand it, most of everything up to 93, are vacuum controlled there are no motors, Just Servos. 

If you hear a vacuum leak in the control area, then your vacuum distributor is faulty. Try to center the control to stop the hissssssss.


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## kdq269 (Jul 9, 2015)

*Vacuum Leak*

I've been researching on You Tube and other sights for days. I've heard a can of carborator cleaner is highly flammable and is not the safest method. If you do use this method have a fire extinguisher closer by. The best way seems to be with a propane cannister with a hose attached. You do NOT light the cannister. While the car is running and the cannister is on, you move it along the vacuum hoses, connections and seals. When you pass over a leak apparently the motor will start to run normal because the fuel/air ration returns to normal. I just changed all my plugs, wires and foots, and coil mechanism and my car still won't work. I believe its a leak and now have to go get a propane tank! I'll let you know how it goes!


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## briano1234 (Feb 20, 2004)

kdq269 said:


> I've been researching on You Tube and other sights for days. I've heard a can of carborator cleaner is highly flammable and is not the safest method. If you do use this method have a fire extinguisher closer by. The best way seems to be with a propane cannister with a hose attached. You do NOT light the cannister. While the car is running and the cannister is on, you move it along the vacuum hoses, connections and seals. When you pass over a leak apparently the motor will start to run normal because the fuel/air ration returns to normal. I just changed all my plugs, wires and foots, and coil mechanism and my car still won't work. I believe its a leak and now have to go get a propane tank! I'll let you know how it goes!


Placing your year and model in your profile as well as the general area of the world that you live in goes long way in reminding us what you are working on.


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