As I'm sitting here dismantling the spare upper intake manifold & throttle body, I came up with a few observations & questions. I have no reason to believe this throttle body has ever been tweaked or adjusted, so I suspect my observations will hold true to most S4 throttle bodies.

First, the vacuum actuator for the double throttle system seems to be leaking. I checked this because a friend of mine mentioned that he tested his & it was leaking. This represents a vacuum leak. It's small, and goes through a bunch of things to get to the engine, so it probably won't be terribly noticeable - but it's still worth checking, and could still cause some idle fluctuations.

Next, the secondary throttle plates don't appear to open fully. They get to 90% or so, but with the primary plate wide open, they are not fully open. I suspect this does represent a power loss at high throttle settings.

On to my questions.

At highway speeds (75-80mph) the secondary plates are slightly open. Would adjusting the linkages so they remain closed at this speed improve fuel economy at all by allowing a higher primary port velocity?

Alternately, how does one adjust the throttle body so the secondary plates open fully? It appears that they can be adjusted to open with the primary plates, but then one would lose some of the low throttle smoothness that the sequential opening provides.

Or is it just not worth worrying about?

-=Russ=-

 

Replace it or remove the double throttle system entirely. On the NA this won't have any performance benefits like it does on a Turbo, but it's only there to stop you romping on the engine while it's cold, which I'm sure you wouldn't do...

That last little bit of movement makes very little difference to flow. The stock TB is huge for the NA's output, so removing this tiny restriction would have basically zero effect on power.

Possibly, but it's also safe to assume Mazda spent quite a bit of time figuring out the best point at which to start opening the secondaries. The actual decrease in fuel consumption from increasing primart port velocity is going to be miniscule, if any at all, but it will cause further restriction in the intake tract requiring more throttle to make the same power. You'd be going in circles, but not achieving anything.

Correct. Having all the throttles open together would have a negative effect on drivability at low throttle openings, in part for the same reasons you were thinking of above (port velocity).

That would be my general feeling.