S4 B7 Intake Manifold Flap fixed open.....better throttle?

B6/7 S4/RS4
#1

Ok, so a bit of a click bait title, my bad.

First things first, car is an S4 B7 with an ecu tune, homemade piggie pipes (front cats smashed out), and miltek cat back.

Basically, been checking and testing a few things recently, and for one reason or another, fixed the intake manifold flap in the open (high rpm) position by removing the vacuum to the actuator…Knowing that the power should be down, I was a bit surprised with the result.

Firstly, the exhaust sounds nicer??? Much deeper v8 sound. Secondly, the initial throttle response below 3K rpm is actually better??? Flap isnt designed to open below 5K, so have a dead band between 3 and 5k. If I reconnect the flap actuator to how it should be, the throttle response is worse up to 3K, and obviously better after that. I’ve been trying to trace a tiny supercharger whine as well, and that seems to go away also lol (I know these engine’s whine, but I’ve got a good ear for things).

Now the “better throttle response” that I’m talking about isnt massive, but enough to notice. As well as the engine sounding much nicer, I’m a bit confused lol. Other than the mid band power, the car just drives and sounds sooo much nicer…WTF?

So for any techy gurus out there, whats your thoughts? I appreciate the engine is setup for the two different power bands of the intake flap, so is it just a coincidence that its better low down? Or what I’m wondering more, is that there’s something wrong somewhere, and for some strange reason, this has shown it up?

Thanks all. I know this all sounds a bit odd, but I’ve seen the odd mention of something similar before, and everything I say is 100% happening!

#2

Hi rambo.

The S4 flap is one of the more simple designs. As it’s just one big lever that swings up and down as you have seen. When they become less functionally stable they cause a bit of issues power and drive wise.

The flaps tend to get caught in this not really open not really closed situation and that causes turbulence and then just a blockage of the intake path. The runner length change will effect the exhaust and intake tone due to the fact that there probably was a decent restriction.

Also there is a chance that you might have the flaps in the long runner position and think they are in the short runner. I think if I remember and I can go check on my car but the default is actually short runner not long. That might be one thing. But the good part is the car sounds like it’s running better and that is always a good win.

#3

Hi Justin

I was hoping you’d reply :slight_smile:

Arm down is the high RPM position which is the default spring position. Arm raised to about 75deg is the low RPM position. So it defaults via the spring to the short runner position, which is why I’m so confused regarding the slight increase in low down power lol.

The car was running smoother, and sounded nicer, but overall “technically worse” because overall power was down because of the dead band in the middle. I’ve reconnected the vacuum line back for now, as cant be without that overall power haha!

It just didnt make any sense to me why it felt slightly better low down, but the physics of intake manifolds is far more than just air in lol, and way above my thinking haha.

With the engine running, and the flaps pulled by the actuator to the long runner position (ie all connected and operating stand alone), I can still force the arm just that little bit more (which also stops the slight flap rattle which is so common.

So from that, I’m wondering if the flaps just arent seating 100%, which is making it feel slower than maybe it should be. Either that, or the vacuum is letting go under load, as I’ve tested the vac system to death while stationary lol.

#4

I would remove the intake and then with the throttle body off do a vac test and see if the actuators are holding and functional in the entire range. I think an intake off vac test and visual understanding of where the flaps are and if they’re restricted will give a better idea.

The flaps and actuator system are prone to all kinds of issues including the screws for the flaps backing out.

#5

Ah interesting about the screws. I know the flap is prone to seizing or wearing in the guides, but didnt know the screws backed out…I thought they were plastic?

I’ve already tested the actuator, and it holds 20in/mg for 5mins, so I called that a pass lol. But I’ve definitely resigned myself to dismantling the intake manifold, although as you say, I’ll have a good look and checkup first once its off!

Original reason I started faffing with all this, was the slight whine/whistle noise, which is still there. With everything else I’ve done, I’ve narrowed it down to either the intake, the cam cover gaskets leaking again, or its just the noise of the piggies lol

#6

Well, haha, this is kinda embarrassing really, but I found the problem.

Turns out, it was the Pipercross foam panel filter blocked lol (well not fully blocked, but not letting the full flow through). I’d cleaned it not that long ago, so it never even crossed my mind. Bank 2 had been running ever so slightly rich, but bank 1 was fine, and no codes etc. Obviously it had enough and decided cleaning wasn’t good enough lol!

Went and bought a K&N, and noise and power are back to normal. Explains why the noise changed so much with the manifold flap in the open position!

#7

Interesting, Still good job getting to the end of the issue.