Strange problem after fill up

[dewok]

Every time after I top off my tank my car seems to run a lot rougher, for about a 1/4 tank then it levels off some.

I just replaced my fuel filter a few weeks back, new plugs and air filter too.

Why would this be happening?

--2005 1.8tq tip 36k miles

[Tugboatguy]

When you top up do you stop when the pump kicks off, or do you add more gas after that? If you add more that could be you problem , new cars fuel systems don't like it when you do . Something to do with the vapor system, If it Just started and you go to one gas station try a different one the pumps may be over filling .

[dewok]

When the pump kicks it off the first time, I always stop. A few years back I heard it was really bad to keep topping it off after the pump stops it the first time.

I was just reading that the EVAP system can cause this if the N80 valve is on its way out, I have no codes, and vag com scans my ECU with no problems. All the Readiness tests passed too.

[dewok]

I found a replacement N80 valve at ECS for $90, but before I pull the trigger maybe someone else has had this same problem and can comment.

Full tank - car runs like crap but no CEL

3/4 tank to empty - car runs normal


and by "runs like crap" i mean the engine is very loud, a noticeable drone on the highway at all speeds, vibrations at idle (while in D)

[HTA A4]

Sounds more like some sort of exhaust leak... But it doesn't make sense that it's only after you fill up

[dewok]

Found this on vwvortex: http://forums.vwvortex.com/zerothread?id=3983107

"N80 valve ( Evaporative Vacuum Purge Valve ) is likely leaking. Same thing happenned to my Audi. Wouldn't start after fueling. Car acts like it is fllooding.

What happens is that valve sticks open and when you refuel, all of the fuel vapors go into the Evap Canister ( Charcoal Canister ) . The N80 valve is located between the Evap Canister and the Intake manifold and is suppossed to be closed when the engine is off. When you start the engine, the N80 valve " cycles" ( that's the "clacking" or " clicking" sound you often here under the hood for a few minutes ) and the fumes are slowly sucked into the Intake Manifold at a controlled rate.

When the N80 valve fails, it usually sticks open. So all those gasoline fumes flow directly into your intake manifold when you fill up. Then car doesn't want to start and will run rough. After starting, a faulty N80 valve can alos cause a " mystery" vacuum leak and trip a long term lean fuel trim code.

Overfilling the gas tank is a no no on our cars. This can flood the Evaporative Canister and flush carbon particles into the N80 valve which causes it to stick open."


While I dont have problems starting my car, its possible that my N80 is only partially stuck open. I'm going to do some vag com logging tomorrow and see if I can see any funkiness. I would assume I can look at the fuel trim after fill up then near empty and they should be very different correct?