My EVAP canister purge valve throws a fault code on dashboard from time to time and after couple of days of driving check engine lamp is gone all by itself. After driving my car for a few days more, it throws a fault code again on dashboard. I've noticed an increase in fuel consumption too.

There is no smell of gasoline around the car nor in the engine bay. When I open a gas tank, there is some kind of noise which won't stop (I was listening only for a couple of minutes) and it sounds like there is some kind of suction, but I'm not 100% sure in this sound description. 

It is easy for me to replace EVAP canister or a valve, but I'm not sure that I will solve the problem because of the possibility of leakage somewhere else in the system?

Do you have any advice for me what, and how, to check before buying new EVAP?

Thx in advance..

I just removed mine.

 

http://www.pimpmyskoda.co.uk/V2Images/ModsEngine/EvapRemoval.htm

 

But if you do need to replace it there are a few cars being broken for spares in the for sale section, you should get one for a reasonable sum.

Thanks mate, but I'm not sure is it valve, canister, hoses, etc.. I wold like to get to the bottom of this to be 100% sure what is the problem.

Edited 16 July, 201312 yr by mister8ight

Got rid of mine as it ticked so loud and looks better without it... All you need is a resister, a small length of tube to route the open connector away from the engine bay and to bung the vac line

Take out yours and shake it, the charchol should be moving around inside, mine was solid.

 

Either that or the valve itself is knackered, do you have VCDS ??

You can run an output test to see if it's working.

Thx mate, will do that.

We have reset the error and run the test right after and it passed the test.

It's throwing faults from time to time, not always

I'm driving for four days and it's ok...for now.

Do you brim the fuel tank by pressing the nipple inside the fuel filler neck?

To be honest, I don't get your question 100 % (not a native english speaker), but I must say that I don't do refueling at the petrol station. Workers do and I really don't know what they are doing with this nipple inside the neck. I prefer keeping my tank full and usually fill it until it clicks and that's it, but some times I fill it all the way up to the neck when I take long trips (few liters more - very rarely).

I've been looking this nipple right this moment and realize that it couldn't be pressed directly from above, it can only be pushed down towards tank flap. When I push down this nipple nothing happens (no sound). Also, there is no sound this evening when I opened the tank like it was last night and I just came from a short trip (30 km).

Edited 16 July, 201312 yr by mister8ight

I asked because I have read that if you overfill the fuel tank by venting the air in it by pushing the nipple downwards with the fuel nozzle, then over time this can lead to damage to the Evap purge canister. There is no noise when you push the nipple downwards.

Thank you for that info! I'll take care next time

Pull the hose that runs from the block of three fuel lines to the cannister, blow/suck through it, it should be a one way valve.

If thats open it knackered and needs changing.

Thank you very much for this info 

Went today to the mechanic and this is the fault code (see pic):

I was told that this is EVAP valve but I'm not very much familiar with diagnostic codes (yet )

Could this be a second lambda (after the CAT)?

First lambda (OEM) and the CAT are brand new.

Edited 20 July, 201312 yr by mister8ight

Have a look at the Ross-Tech Wiki entry below for that fault code.

http://wiki.ross-tech.com/wiki/index.php/16556/P0172/000370

Thx mate.

Lucky me..it's just a half of a car of possible faults 

Edited 21 July, 201312 yr by mister8ight