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So I've been clearing this code on my wife's 2002 Cabrio on a regular basis. Things I've tried to fix this is replace the gas cap (purchased at the VW dealership for $50!) and hunted down two Vacuum hoses that were disconnected.
I found one hose that connected to a white plastic tube and went into the firewall near the heater hoses behind the ignition coil. Cleared the code and after several days it came back.
I checked again and found another vacuum hose that connected to a fitting on the intake near the TPS. Cut off the worn end and hooked it back up. Cleared the code again and am now waiting for it to happen again. This was 2 days ago, so it will probably throw the code tomorrow.
I checked under the passenger rear side of the car next to the rear wheel and verified that all the hoses and connections there are fine. I also followed the plastic tubes under the car to the engine compartment to make sure that there are no disconnects there.
Anybody have anything else I can check?
If it helps any, if I do not clear the code, after a few days, the car will throw misfire codes and the engine will begin to stumble. Let it go too long and the car will act like it's going to stall. Clear the code and everything runs fine.
Oh, one other thing. The airpump rubber mounting posts were all rotted out and the airpump was only being held up by the connecting hoses and the metal bracket it sits in. I replaced the rubber mounting posts with new ones and remounted the airpump back the way it's supposed to go. Would this cause a P0455 code to be thrown?

Thanks
 

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Sounds like a repeat vac. leak issue becoming more common as heat and time are deteriorating the hoses in the engine bay.

You could have a shop with a smoke test and proper Vagcom locate the leak if it comes back, pay their 1 hour diagnostic charge and fix it yourself, otherwise you can keep guessing and fixing what you find as you are.

The P0455 is a large Evap leak. Probable cause is Hose connection(s), Intake leak, EVAP Canister, EVAP canister purge valve. Check your evap canister, purge valve, and keep looking for worn/loose hoses if you do not smoke test it.
 

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Smoke test

Hmm, this seems interesting:

I don't smoke cigars, but it might be worth puffing on one to see if I can find the vacuum leak!

Has anybody else ever done something like this?
 

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Sounds like a repeat vac. leak issue becoming more common as heat and time are deteriorating the hoses in the engine bay.

You could have a shop with a smoke test and proper Vagcom locate the leak if it comes back, pay their 1 hour diagnostic charge and fix it yourself, otherwise you can keep guessing and fixing what you find as you are.

The P0455 is a large Evap leak. Probable cause is Hose connection(s), Intake leak, EVAP Canister, EVAP canister purge valve. Check your evap canister, purge valve, and keep looking for worn/loose hoses if you do not smoke test it.
Thanks for the input on this. I’m working on my son’s 2012 Golf Base and it showed a P0455 and P0454(small leak). I relaxed the purge valve and cleared the codes. It done well for a couple weeks, but now the P0455 code is back, but not the P0454 code.
I’d prefer to fix this myself is possible, but don’t want to keep throwing money at parts of a better mechanic can more quickly and easily identify it. Is the next most likely culprit the charcoal canister, or would I be better off biting the bullet and letting a professional look at it?
 

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Smoke test

Hmm, this seems interesting:

I don't smoke cigars, but it might be worth puffing on one to see if I can find the vacuum leak!

Has anybody else ever done something like this?
Tech_ed - a little late to reply to your comment from 7 years ago, but I just wanted to thank you for posting that video for the idea of the cigar smoke.
I took off a vacuum line connected to the n80 valve, blew cigarette smoke through, and it worked. It showed me where my leak was coming from!

MK4 -2000 - GTI - 1.8t
I was having a P0442 code for a small leak and it wound up being the charcoal canister (after replacing the n80 valve, and all the egr valve vacuum hoses). After replacing it I didn't plug in one of it's hoses all the way (the plastic hose that you have to press very firmly into the hole with the clip) and started getting the P0455. But because of your suggestion I was able to locate the leak almost immediately ( after removing the rear passenger wheel and fender liner of course.)
 
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