TimZ

Hey guys, at idle when I push the S button, I can hear the baffles open in the exhaust system as normal. When I slowly raise the rpm's up to just over 1000 I can hear them close. Then when I let it back to idle they open again. At first I thought it just does that when the car is cold but I tested it when at operating temp and it does the same thing. This ever happen to anyone else? Looks like I need a dealer visit.

Thanks for any help
Tim

petoria

I think that's normal operation. Mine does it too...

ELEVENS

In "S" mode, I think the flaps are supposed to stay open. Pretty sure that mine do.

In non-"S" mode, the flaps are open at startup, then close, then open again under certain high-power conditions (something like >5000rpm and full throttle ?).

Engine vacuum pulls the valves closed. That vacuum is "stored" in a vacuum canister at the rear of the car. If the flaps are closing in "S" mode, maybe the vacuum switch isn't sealing (closing) completely. Just a guess.

stong

I pulled this from Audi "Self Service" training manual I found on the web:

"Exhaust flap control Audi RS4
A further difference is the layout; one exhaust flap is Function located downstream of each of the rear silencers.
The exhaust flaps are fitted to give the engine a sporty sound. The exhaust flaps are switched in such a way as to meet the statutory limits for vehicle exterior noise.
Low-frequency droning noise at low engine RPM is prevented. At high engine RPM and high exhaust- gas flow rates, flow noise and exhaust backpressure are reduced by opening the additional cross- section.
The exhaust gas flaps are closed at idle, low engine load and at low engine RPM.
The exhaust flaps are switched by a vacuum actuator. Both vacuum units are switched by an electrically activated solenoid valve. The exhaust flaps are switched according to a characteristic map.
The factors of engine load, engine RPM, gear selected and the shift signal from the Sport button are used to plot the characteristic map.
For example, the exhaust flaps are opened at idle when the Sport button is pressed."

Seems the flaps are vacuum controlled, but the vacuum is controlled by a solenoid. If I'm reading this correctly, in non-S mode with high load and high exhaust rate, the flaps open anyway. I remember reading elsewhere that the main reason for the the S mode is to open the flaps to make it louder at idle - no real performance gain.

TimZ

Thats exactly what I was looking for. Thanks a lot! Its still a little confusing but at least I know now that there's more than just open or closed with the S button on or off. Sounds like there's 2 flaps that are operating separately depending on conditions and/or S button.

Thanks

Coupon

The S-button should also give you sharper throttle response in addition to opening the exhaust flaps. Not quite all for show.

Reggie

Yep - the response is changed - and yes the flaps do close in S-mode at different rpms