B6(7?) S4 Exhaust Flap Vacuum Leak

B6/7 S4/RS4
#1

For those of you with a B6 S4 (some early B7s??) with the vacuum actuated flap on the stock exhaust and have added an aftermarket exhaust it may not be sufficient to just plug the vacuum lines to the mufflers.

With this system there is a vacuum accumulator deally in the trunk on the driver’s side (behind side panel). With the back seats folded down you can hear it bleed off a bit of pressure when the rpms drop below 1700. I’ve had a suspicion the car was not running perfectly for a short while now and this past week I had my seats folded down and could hear the accumulator but is sounded broken so I pulled the side panel off, removed the ridiculously elaborate bit of nonsense and capped the line from the motor very thoroughly.

The car is now much smoother at idle, requires much less throttle when pulling away and is generally running smoother.

Coles notes: Remove the POS and cap the line well if you have a B6 and an aftermarket exhaust. Peace.

#2

When I installed my exhaust I just connected the 2 ends of the vacuum hoses to each other rather than capping them each off. It seems to have worked pretty well. What kind of sounds was it making that made you worried about it? I’m curious if my method was the best way or at least a good way to go.

#3

The normal sound from the vacuum reservoir in the trunk was a quite audible ppssshhtt as the tach dropped below 1700 rpms but recently it was just a lot weaker sounding, almost imperceptible. That was the 1st clue that it was going bad. Combined with the slightly rough running at low RPMs lead me to believe it was on the way out and was giving me a week vacuum leak/issue of sorts.

Removing it was pretty easy, the biggest pain was just getting the side panel off in the trunk but all in it was a 15-20 minute job. Bonus perk - you’ll save a couple of pounds as the stupid thing really is quite elaborate. I’d pull it out even if it seems to be ok simply because it is easy and reduces the likelihood an issue pops up later. I’m thinking that by capping the lines at the exhaust it simply strains the thing and over time it wore out.