# HELP with 2001 Jetta 2.0 AEG engine misfire/vacuum leak!



## Fsikorski (Feb 1, 2010)

So I have a 2001 Jetta 2.0 AEG engine. I just installed this used engine. It has new timing belt, plugs , wires, coil, crank sensor already. I installed it with newoil, filter and coolant.
Now, when I start it when cold.....it has a occasional misfire. It is fine once its warmed up, but when cold its misfiring every 3-5 seconds.
I also noticed what I thought was a vacuum leak. It turns out there is no leaks......but the little vacuum line that attaches to the air intake tube.....right under the big hose connected to the oil cap housing, it sound like the hiss of a vacuum leak while at idle. I can pin the line and it stops the hiss. I have a check engine light on, and a Evap code, so I think its related. I also think it might be contributing to the cold start misfire.
SO.....is this thing....this small valve that the small vacuum line and the larger one from the oil cap housing plug into.... or whatever you wanna call it supposed to be open all the time? Is this constant hiss normal from it? If I pinch the line the car idles better so it seems something cant be right with it. There is also a 2 wire connector on this thing.....so it has to do something~
Any info from other with this issue?


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## Fsikorski (Feb 1, 2010)

*Re: HELP with 2001 Jetta 2.0 AEG engine misfire/vacuum leak! (Fsikorski)*

Maybe a pic would help explain!


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## Fsikorski (Feb 1, 2010)

*Re: HELP with 2001 Jetta 2.0 AEG engine misfire/vacuum leak! (Fsikorski)*

NOt one bit of info eh???


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## vdubbugman53 (Nov 7, 2006)

*FV-QR*

put that hose back on the intake mani...where does the hissing hose lead to? find out and plug it back in


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## Fsikorski (Feb 1, 2010)

*Re: FV-QR (vdubbugman53)*

That picture is not of my car.....simply using it as reference. The hose is NOT unplugged.....I have traced it down and it is connected and has NO hole/cracks in it. 
I think there is an issue with the PCV heater.....which is whats connected there. If I pinch off that small vacuum line the hiss stops.....which makes me think it shouldnt be free to draw air all the time.


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## KLGreene (Sep 9, 2010)

So, anyone know what that VAC line is supposed to be doing? And is the hissing sound coming from it at idle normal?


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## vwguy3 (Jul 30, 2002)

I'm pretty sure that valve is the PCV valve and I don't think that it should be open all the time. I believe that you can take the whole intake tube off (because its all one piece) and clean the valve with carb cleaner. And if that is stuck open. Maybe you should get some MAF sensor sleaner too and give your MAF sensor a good spray. That should clean up your misfire.

Good luck.
Justin


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## KLGreene (Sep 9, 2010)

Well, on a 2.0L AEG, is the PCV valve that large round piece of plastic underneath the oil cap or is it on the intake tube itself?


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## vwguy3 (Jul 30, 2002)

I was told that the PCV valve is on the intake tube and the thing under the oil cap is called a water seperator valve. If that is leaking there is a gasket under it that is the same one that is on the oil cap.


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## vwguy3 (Jul 30, 2002)

So did you figure out? what did you do?


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## KLGreene (Sep 9, 2010)

Well the problem is a rough/varying idle where periodically the RPMs drop quite a bit. The thing is that this would only occur if the car is stationary. If the car is coasting at a high enough speed though (in neutral), the idle is perfectly level at 800 RPM (no movement in the needle at all). Then, once the car slows down and comes to a complete stop, the RPM variation / rough idle returns...


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## Slimjimmn (Apr 8, 2006)

That is supposed to hiss.
Check compression, its an aeg....


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## KLGreene (Sep 9, 2010)

Meaning that AEGs in general have compression issues? Wouldn't compression issues manifest themselves into more visible problems at higher RPMs (i.e. not just idle)?


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## Slimjimmn (Apr 8, 2006)

low compression would cause hard starts and cold missfires. As the engine warms up (parts expand from heat) and builds compression it runs better. AEG's are common culprits for piston ring issues and oil consumption. Easy to check and eliminates mechanical issues.


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## KLGreene (Sep 9, 2010)

I see. Yeah, it would be easy to check compression, but I guess ultimately fixing it (if for example it's due to poor piston rings etc) is another story entirely.


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## Slimjimmn (Apr 8, 2006)

its very easy job on a 2.0. If you can change a t-belt you can do a HG on one. :beer:


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