clayne

This was originally inspired by RETed - I must give credit where credit is due.

Given enough time, the FD secondary throttle plate linkage will develop excessive play and runout in the dowel-pins and linkage arms present on the throttle body. This obviously steals air volume by increasing the throttle restriction.

There is a simple "fix" for this that requires bending the tab on the secondary throttle plate shaft key to reduce the amount of at-rest play present in the linkage.

I bent the tab by applying a small amount of "twist" to the top of the tab, just enough to provide about 2-4 mm worth of increased deflection. I also tightened down all of the throttle plate shaft bolts with the linkage mechanism just on the *virge* of moving the plates - as this reduces the amount of play present between the shaft keys and the rest of the linkage. Basically it reduces the time to actually get the linkage moving the plates rather than the rotational assembly rotating excessively before actually rotating the plates. As you can tell my TB was never removed from my IM ever since I've owned the car, as it was still sporting the original green paper gasket. I think most people will find a decent amount of slop present in their secondary throttle plates if they take off the air extension arm and watch while manually actuating the entire mechanism like the cable would.

(all pictures clickable thumbnails)

Before:




After:




One of the culprits:




The actual mechanism that develops slop. My index finger is pushing the pivot point upwards through the area which develops play when it is fully extended. Normally it would lose extension due to slop in the pins, etc.:

Fatman0203

Why not just pull out the dumb double throttle?

NewbernD

iTrader: (1)

It's not the double-throttle, it's the secondary throttle plate linkage. You can't take those out..

I diagnosed mine as sloppy plastic bushings in the linkage, and did a quick-fix with a piece of silicone tube. (I know.. it's not a permenant solution..)

Ghetto fix

Wargasm

Are we even sure that we -want- the secondaries opening at the exact same time as the primary plate opens? On the old FC turbos, Mazda actually SPECIFIED in the manual that there was a certain amount of slop or delay that was the "right amount" between when the primary and secondaries started moving.

Brian

Wargasm

Follow up... my suspicion is that Mazda wants the primary to open by itself on small throttle openings to keep air going through the smaller primary intake/ports which would make it drive more smoothly around town. Perhaps if you have all three going at once it makes it too sensitive or something... I dunno. If Mazda really wanted them all open at once, why wouldn't they have just built it in with no slop at all?

Brian

NewbernD

iTrader: (1)

It doesn't significantly change the timing of the opening as much as it makes sure the secondaries are fully opened when the throttle is fully open. With all of the spring pressure on the mechanism that opens the secondaries, all of the plastic bushings get a little sloppy.. and the throttle plates don't fully open any more.

My "before" pics were a little worse than clayne's.. they had a good 5-10 degrees left to open. All that we've done is take the slop up in the linkage.

..Dave

clayne

Exactly.

Leaving the throttle plates with the slop present in the linkage and worn out pins is highway robbery, pun intended!

Brian,

If you look at my "before" picture, that is with the throttle plate mechanism at *full* extension - no ability to open any more. That is what started the little fix, seeing that the secondary plates were not even open all the way at max throttle.

clayne

Wargasm,

You check yours yet? Nice car in your avatar BTW

clayne

BTW: Whenever you take yours off, you will see what we are talking about.

They obviously did build it with no slop, and it just simply wears out.

The plastic dowels wear down, and the washers and rivets lose their strength, allowing the secondary arms to move around too much.

Wargasm

Yeah I've eyeballed mine before... they were very fully open when I looked at them.

B

clayne

They were fully open before?

Just found an old thread while doing some troubleshooting on this issue.

https://www.rx7club.com/showthread.p...threadid=87823

Apparently yours were the same as mine. Angled on full open. What'd you end up doing?

TESTCAR

like wow! jus rip the suckers out completely like everyone else has done 4 years ago!

clayne

Like wow! We're talking the throttle body NOT THE UIM.

Look at the pictures.

Sesshoumaru

iTrader: (1)

The FC were a bitch about the timing of air.

Mine didn't like it after removing the other set of secondary butterflies in my TII

If i floored it under 3k my car would bog and then take off in about a sec.

This is inpart due to the ecu. With the change in metering i think FD's won't have a problem. Before it was a problem.

i wish i could find a tb for my s4 cheap

I have noticed this in my tb also but didn't think it was deemed manditory.

I was more concerned with the butterflies closing 100 percent.

TESTCAR

did I mention the UIM did I , sorry

duboisr

When the little plastic bushings go bad just make new ones out of brass . Even the ones on the flat rod that goes between the two shafts . They are small but it has been done .

Sesshoumaru

iTrader: (1)

is that a double question?

this is the secondary throttle plates not the double throttle.

if you removed them there would be nothing controlling the air to the engine.

clayne

Well I'm seeing wacky stumble/oscillating idle right around 1300 rpm after putting my TB back in (with a bunch of other crap done) and it's quite annoying. It's not the TPS - I've already adjusted it. After 1300-1500 rpm the steady state throttle is fine.

I'm thinking I may have set the secondary plates to open to soon, as Wargasm mentioned above. Unfortunately dialing this back may prevent the secondaries from opening fulling.

It looks like the only route is to rebuild the linkage, as duboi alluded to. The dowel pins are the issue.

Sesshoumaru

iTrader: (1)

if it is at idle your butterflies should not be open at all so when they open is not a question.

unless i'm missing something here.

you could have opened your butterflies a bit more when they are at rest with out knowing it and allowed more air altering your idle (most commonly done with the set screws).

using butterflies to set an idle is trick buisness. One thread turn can mean 100rpm. I set my TII idle with no BAC or idle controllers. Just butterfly position so i know they can be picky

clayne

Alright, it's not the secondaries at all.

The engine, upon reaching 1300 rpm exhibits a very bizarre stumble, up and down, that goes away past 1500 rpm. It's only between that range that it bounces up and down.

Secondaries aren't even being moved with the lever arm by 1300 rpm, so it isn't them.

clayne

What else is f'ing annoying is that it does not do it with electrical load (fans on).

CapitanCombo

I had the same problem
on full throttle the secondaries were NOT fully open
I tried to fix as Clayne did but with no chance, it was still too low.
Doing this also made the secondaries to open at the same time of the primary, this is bad.
This is a staged 3 plates throttle so secondaries must open with a angled delay.
So I changed the linkage to make secondaries open fully but still keeping them staged.
Worked fine but this seems to have increased 3K hesitation

CapitanCombo

More or les I think I am getting a "bog" like sesshoumaru has on his FC
I think this is due to secondaries opening and not matching with secondaries injectors switching on

clayne

Well with a PFC all of this can be tuned out. But I'll continue tracking the problem tomorrow. I'm sure it's something scientifically plausible.

Keep you up to date.

NewbernD

iTrader: (1)

Sounds like you have a vacuum leak somewhere. The fast idle and the oscillating fast/slow idle are the clues.