# MK4 2.0L 8v vacuum leak?



## ZeRo_C0oL (Aug 27, 2002)

I went to the dealership last week to get my pathetic gas mileage diagnosed, and they refused to replace my o2 sensor under recall, claiming that my o2 sensor was fine but the bad mileage was due to a vacuum leak. However, on my invoice, it says "may need rear o2 sensor." Anyway, how can I find out which vacuum line is causing the problem? How many lines are there? They said it was going to be about $50 for them to do, and I figured I could get the part and put it on myself for a few bucks, at most. I can't imagine replacing a vacuum line to be real hard. Would I be better off getting ripped off and having them do it, or is there some way I can find out which one to replace?
Also, what should I do about the o2 sensor? Regardless of what they say, I'm sure it's bad! And my year had an o2 recall, but they refused to replace it. Is there anything I can do about that? They said it was fine, but again, the invoice says "May need rear o2 sensor." I hate dealerships!


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## StevenT (May 28, 2002)

*Re: MK4 2.0L 8v vacuum leak? (ZeRo_C0oL)*

I once had a leak on the hose that goes from the side of the intake manifold to the FPR. The car ran like crap (no power on freeway) and mileage was terrible. After I got to Napa I got a foot of 1/8 vacuum house replaced it in 1 minute and it ran good.
The easiest thing is to go into the dealership and ask them what hose it was. If they don't tell you, that means they are probably full of ****. I can't do alot of work on my car because I don't have the tools, but whenever I get work done I always get the mechanic to talk to me about it.
If the mech can talk about it then they are full of shat. You're a paying customer you have a right to know what work they are doing on your car.


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## ZeRo_C0oL (Aug 27, 2002)

I asked for a part number, and the service manager said there was no part number... Really, he's a jackass and is never much of a help. I guess they just think I'm a stupid kid.
I know there's a vacuum leak though. I was tooling around with the car today, and I popped the engine cover off and started the car up. I can hear the leak, but can't locate it. Once it gets vacuum (runs for a few minutes), it runs alright but I have no power and ZERO gas mileage. I can smell it running rich. Before it gets vacuum though, the whole thing kind of shakes, and today when I started it up, it was idling REALLY rough and would die several times... finally it got to the point where it would run on its own, and finally got vacuum. Everything shakes up until that point, and it's driving me crazy.


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## Robman044 (Sep 11, 2003)

*Re: MK4 2.0L 8v vacuum leak? (ZeRo_C0oL)*

The reason they said that you may have a bad o2 is because they can't be sure until they repair the vacuum leak. The vacuum leak could be throwing off the o2 reading. If you want to try to find the vacuum leak yourself, get a can of propane and trace the vacuum lines with the can. While doing this take a digital multi millimeter and connect it to the o2. When the propane passes over the cracked, split, ripped or whatver, the o2 reading will read extremely rich over 900 mV.


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## 2000GIV (Aug 19, 2003)

just pull off each line and cap with your finger there is only about 6 or 7 different lines should be easy to find


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## DJKeebler (Dec 6, 2001)

*Re: (ZeRo_C0oL)*

One trick I learned a long time ago about trying to find vaccum leaks is to use a straight straw. Put one end to your ear and move the other end around the vaccum hoses. You should be able to hear the leak if the straw moves over it. This isn't a sure-fire way to diagnose it but it's worked for me a few time. The only other thing I could recommend if you can't find the leak is buying a bunch of vaccum hose and replacing all the hoses. Good luck!


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## jmullman (Aug 20, 2001)

Yeah, I had this exact problem a long time ago. It's the line coming off of your intake manifold going to your Fuel Pressure Regulator(like the other guy said). Just get some hose and put that puppy on there.
Side note: I noticed that the hose in question was really too short for the application and had dried to the point that it turned to dust as I attempted to remove it. Put just a touch more than you think you need on there and make sure to keep it clear of kinks etc.


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## JOHN-E-GTI (Apr 2, 2001)

*Re: MK4 2.0L 8v vacuum leak? (Robman044)*


_Quote, originally posted by *Robman044* »_The reason they said that you may have a bad o2 is because they can't be sure until they repair the vacuum leak. The vacuum leak could be throwing off the o2 reading. If you want to try to find the vacuum leak yourself, get a can of propane and trace the vacuum lines with the can. While doing this take a digital multi millimeter and connect it to the o2. When the propane passes over the cracked, split, ripped or whatver, the o2 reading will read extremely rich over 900 mV.

this guy is da man!!! that is true tech advice.... it's even more fun making the car run using the propane/vacuum line method.i was happier than a kid in a candy store when i learned that one.


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## 2kjettaguy (Dec 24, 2000)

*Re: MK4 2.0L 8v vacuum leak? (JOHN-E-GTI)*

Be sure to check the line which goes from the EGR valve to the control solenoid on the top righthand side of the engine bay. Where it connects to the valve on top of the header the vac line tends to "bake", become brittle and crack. My car went crazy one day and this line turned out to have broken off.
Good luck http://****************.com/smile/emthup.gif


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## vdubVR6-Munich (Aug 14, 2002)

*Re: MK4 2.0L 8v vacuum leak? (2kjettaguy)*


_Quote, originally posted by *2kjettaguy* »_Be sure to check the line which goes from the EGR valve to the control solenoid on the top righthand side of the engine bay. Where it connects to the valve on top of the header the vac line tends to "bake", become brittle and crack. My car went crazy one day and this line turned out to have broken off.
Good luck http://****************.com/smile/emthup.gif 

I had the same problem. Every time I would start the car this whistling type of sound would come from underneath the manifold. Checked the vacuum hose and it was cracked. Went to the dealership and got some vacuum hose ($3 a foot), and replace it. Hope this helps. GL.


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## ZeRo_C0oL (Aug 27, 2002)

I took it to a shop yesterday and he hooked up a diagnostics program called "VWTool" ...he says it basically functions the same as VAGcom, but is much simpler. Anyway, it threw 10 CODES!








It was logging a misfire in every cylinder, so we came to the conclusion that maybe plugs and wires will fix THAT part of the problem. He replaced the hose from the FPR to the manifold, and that cured the vacuum problem... however, my gas mileage is STILL crap.
He could not get the Evap. and Secondary Air System to run the test, so I'm not really sure what that means. He cleared the codes and reset the CEL, but it came back on during my short ride home. 
So what now? New plugs and wires, and then have the dealership replace the o2 sensor under the recall, if they will? Can't afford to drive this car like this anymore.


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