I recently replaced the turbo on my 2004 A4 1.8. In the middle of the process I found a vacuum line hanging, couldn't find it's connection, so I plugged it. After a few days the car would start, but die immediately. I replaced the alternator, fuel regulator (so also filter), and will next do the fuel pump. Problem still exists, so I thought it might be that line. I looked the part number up and it's the vacuum air cleaner line.

Could this be causing the problem?
And sorry if I sound dumb but where does the dang thing go??? I've spent hours underneath and looking at diagrams online I cannot find it!

In the attached picture it's the three-way valve with the gold plug.
Thank you

 

I see that someone has eliminated the factory air filter box and replaced it with one of those K&N cone filters. While I like K&N Filters, why people just don't use a K&N Filter that will fit the factory air box puzzles me because those exposed cone units allow hot air from under the hood to be sucked into the intake. These things may look cool but, I think there is less surface area on these filters than the larger one that would have been there from the factory. Plus the factory air box is designed to pull in cooler air from the front of the car.

Anyway, having said that, it appears that is the fuel tank vapor purge valve circuit. That end that is plugged up, used to go to the airbox that is no longer there. However, it is not plugged during normal operation as it uses the intake to suck those built up vapors into the engine to be burned. Try removing the plug and see if the issue goes away.

Before throwing any more parts at it, see if you can pull the OBD codes from the computer. That might help point us in the right direction.

 

Thank you for the response! I've tried running it plugged and unplugged--no difference. I thought it was the purge line from the chilton manual--but then the part number said vac cleaner. I've got an OBD reader coming from Amazon so hopefully that will help.

I'm actually posting for my bf (he isn't computer savvy)--he put that filter in there. This car has been a whole bucket of problems, and I'm a Chevy pickup girl so a lot of my knowledge doesn't apply, but he loves it so I'm doing my best to help.

 

Keep us posted and we'll see if we can help out.