Intake manifold butterfly valve?

[FWP!]

I'm a newb with the S4's, very mechanically enclined, and my S4 that I've had a week is raising some questions to me as far as the power band. It seems to have a ton of torque in the lower RPM's, but in the mid range it seems to kinda fall on its face. I have yet to get the coil packs replaced by the recall, but the car idles/drives fine.

If there is some kind of vacuum operated valve that opens up in the intake manifold at certain RPM's, is there a way for me to check if it's working ok?

Another reason is I see someone's been in the engine bay tinkering around, the inlet pipe to the bottom of the stock air box is completely missing, I can look down and see the flapper in the hole which by the way is always open (should it always be open?). Plus I'm having an issue with getting the intake tubing to stay ON the damn throttle body.

Thanks!

[ArthurPE]

if it's like the RS4 the flap opens at a given rpm and speed, it's normally closed
there are flaps in the intake manifold, they deploy at low rpms to enhance torque
not sure if the S4 is the same

[CHECKERED]

if it's like the RS4 the flap opens at a given rpm and speed, it's normally closed
there are flaps in the intake manifold, they deploy at low rpms to enhance torque
not sure if the S4 is the same

It is the same, they call it a variable geometry intake manifold.

I'm a newb with the S4's, very mechanically enclined, and my S4 that I've had a week is raising some questions to me as far as the power band. It seems to have a ton of torque in the lower RPM's, but in the mid range it seems to kinda fall on its face.

what you described is perfectly normal!

[FWP!]

It is the same, they call it a variable geometry intake manifold.
what you described is perfectly normal!

Is there a way to check if they're operating correctly?

[jfunkey]

I would say that if it wasn't working you would get a CEL for open electrical conection

[silverRS4]

Can't speak for the S4 powerband, but comparison's to the RS4 manifold should stay out of this thread for the sake of clarity. The B7 S4 and Q7 4.2L have true variable 2-stage manifolds. The RS4 has a simpler non-variable design ("single length") with tumble flaps. Are the tumble flaps there for torque? The same tumble flap system is also in the Q7 manifold. Why would it have a dual stage and tumble flaps if they were both for the same purpose? The RS4 tumble flaps open at 3500 rpm, yet peak torque is at 5800-6000 rpm. RS4 engines that have the tumble flaps removed (because they carbon up so bad) have exactly the same torque output from 3000 rpm to redline as engines with the tumble flaps. There is one contradicting sentence in the RS4 engine manual -"In contrast to the basic engine (the Q7 4.2L), maximum torque is produced at higher engine RPM. At this engine speed, the intake manifold changeover valve would be switched to the short path for higher power output". This does not correspond to what actually happens, i.e., the tumble flaps open at 3500 rpm while the torque peak in near 6000. There is an Intake Air Switch Over valve, but that controls the power flap in the airbox (opens at 5000 rpm). Also, at the bottom of that particular page, the comment "The RS4 engine does not have a variable intake manifold" was added almost as an afterthought or some kind of clarification that the "switch-over" for increased airflow is occurring in the airbox, not the manifold itself. The tumble flaps IMO, are for the same purpose they are on other VAG cars - low engine speed air charge tumble, reduced emissions and better cold starts. Now back on topic...

[SpeedETC]

I would say that if it wasn't working you would get a CEL for open electrical conection

Not necessarily. I had a buddy's car that had the valve disconnected (not sure how). The lever was popped off the connector to the flap. The car felt extremely underpowered in the midrange, but no CEL.

[FWP!]

Not necessarily. I had a buddy's car that had the valve disconnected (not sure how). The lever was popped off the connector to the flap. The car felt extremely underpowered in the midrange, but no CEL.

Can you elaborate? I'd like to check mine out.

[beemercer]

Is there a way to check if they're operating correctly?

If the flap opens when not under load you could have someone rev the motor to 4k, and you can watch the vacuum actuator piece on the front of the intake manifold and see if it moves.

[Prtaick]

If the flap opens when not under load you could have someone rev the motor to 4k, and you can watch the vacuum actuator piece on the front of the intake manifold and see if it moves.

You can run it with VagCom or a 505x.

[dparm]

The car would feel very slow if it was stuck open or closed.

It gives you the benefit of both short AND long runners in the manifold, meaning a broader powerband. If you were going all-out for a race car (that spends most of its time near redline), you'd do away with the system so that it just gets as much air as possible.

[SpeedETC]

Can you elaborate? I'd like to check mine out.

Take off the front plastic engine cover (4.2-V8). Look straight down and you will see the lever that controls the flap. Follow it to the right and make sure it is connected. Per beemercer's post you can watch it work by having someone rev the car.

[jaybquick@JHM]

The flap is pulled shut by the vacuum actuator at idle and until around 4700 rpm. Turn your car off and look under your hood, it will be open (down). Then have someone start it and the vacuum actuator will pull the door shut (up) thus making the air go through the longer set of runners, which improves torque under 4700 rpm. If it goes up at idle once started then it is working right, that lets you know the solenoid is working and the vacuum lines are ok. Vacuum is just released at 4700 rpm to drop the door again. It even has a reservoir behind the inner vendor to keep vacuum long enough at WOT since at WOT you have no vacuum. The way the system is designed if it failed it would fail with the flap down, which is the way it optimizes top end power. In that case your low end torque would suck.

I think you are just experiencing the factory tune and the factory intake manifold that limits the top end power to aid in optimizing the low end. Plus the tunes are straight limiting up top. We have tunes and a soon to be released intake manifold replacement that gains torque down low and top end. The car actually feels strong above 6000 to 6500 rpm and the motor becomes usable until 7000 or more depending on your exhaust system and tune. If you still have stock downpipes and or cat back you should address your exhaust first. Cat back, then aftermarket downpipes or piggie pipes. We sell those as well as long tube headers for the more hard core enthusiast.

Hope this info helps.

[FWP!]

The flap is pulled shut by the vacuum actuator at idle and until around 4700 rpm. Turn your car off and look under your hood, it will be open (down). Then have someone start it and the vacuum actuator will pull the door shut (up) thus making the air go through the longer set of runners, which improves torque under 4700 rpm. If it goes up at idle once started then it is working right, that lets you know the solenoid is working and the vacuum lines are ok. Vacuum is just released at 4700 rpm to drop the door again. It even has a reservoir behind the inner vendor to keep vacuum long enough at WOT since at WOT you have no vacuum. The way the system is designed if it failed it would fail with the flap down, which is the way it optimizes top end power. In that case your low end torque would suck.

I think you are just experiencing the factory tune and the factory intake manifold that limits the top end power to aid in optimizing the low end. Plus the tunes are straight limiting up top. We have tunes and a soon to be released intake manifold replacement that gains torque down low and top end. The car actually feels strong above 6000 to 6500 rpm and the motor becomes usable until 7000 or more depending on your exhaust system and tune. If you still have stock downpipes and or cat back you should address your exhaust first. Cat back, then aftermarket downpipes or piggie pipes. We sell those as well as long tube headers for the more hard core enthusiast.

Hope this info helps.

I will check out the vacuum solenoid, thanks.

But I think I figured out my problem? In another thread I posted about my intake elbow NOT staying on the throttle body, no matter how hard I tightened the band clamp down. Well I took the elbow completely off, check to make sure there was nothing in the way, re-installed it and it's fine now. Difference? The car drives a heck of a lot better, it was obviously screwing up the a/f mixture since it was behind the MAF sensor. The car has more power in the mid-range so I think I've fixed it?