2002 allroad - NO BRAKES!!
 

Very strange thing happened to me about an hour ago. It's like 19 below right now and windy and I had to run over to my friend's condo to fix the garage door for his renter. On the way home, I went to hit the brakes and pedal was rock hard. Thankfully, there isn't much traffic today and to got things under control with the e-brake but there was some serious puckering going on there for awhile.

When I got the car stopped (still running), I noticed a fairly strong smell of gas INSIDE the car. I also popped the hood, geared up and heard a sizable vacuum leak. I was not sure on which side of the car the noise was coming from, but it was definitely between the motor and the firewall. I started pulling plasic to find the leak but before I got too far I heard the vacuum noise change and then stop, like the noise you'd hear when you suck a tennis ball up with the the shop vac. Anyway, the noise stopped and the brake power returned so I drove home.

This all got me thinking about what could have caused such a set of conditions. If a Kombi valve had stuck or leaked and was dumping some unburned fuel from the exhaust into the engine compartment, it's possible that it got sucked in over on the passenger side air intake. But more importantly, is it possible for the Kombi valve to be at fault.

The car threw codes and while the vacuum leak was going on the CEL was flashing. I will check codes later but I'm sure it's going to tell me that I had a vacuum leak (large!).

Anybody run into this before of have ideas on what to look at?

Thanks.

Could be one of the vacuum lines for the brake system. Perhaps the one that goes between the engine bay and rain tray. Number three in the picture.

http://www.partsbase.org/media/image...2ca984b153.png

Interesting thought. In the past, that connection has leaked a little if the engine side vacuum line (#5 in your picture) is moved around a bit. I'll get out there today some time and play around a little. It's still -17 here this morning but I have a heated garage.

Found it!!
 

This is the culprit which is likely #5 in the earlier schematic.

http://i165.photobucket.com/albums/u...akebooster.jpg

The location of this piece is between the back of the motor and the firewall, directly under the 'Y' pipe where it hangs a left towards the air box.

In the picture attached you can see where the hose that runs to the firewall (right facing arrow) has two little orange "valves" on it and it fits into the plastic cylinder (larger, left facing arrow) lower in the picture. It's just glued in and when the glue gets old and brittle (2002 with 187,000 miles) things start to fall apart. Mine just broke apart. It seems this is a common issue with the S4 guys, particularly guys running high boost (my allroad is stock).