Still trying to sort out what is causing my bouncing idle on my JDM S5 turbo. Pulled the throttle body off again today and took a look at it. Should note here that I've done the throttle body mod with the secondary plates removed, and all the cold starting stuff pulled too.

When I look at my throttle plates the top one is closed fully, and can be adjusted using the throttle stop screw. But the lower ones seem to be open a little. Is this right? I also couldn't work out how I am supposed to change the gap of them at idle. The plates do work correctly when opened (i.e. the top one opens a little and then the lower ones start).

Cheers in advance

 

i dont think so if anything your primary should(top single plate) should open before the bottom secondaries ,by like 3/16 of an inch. my idle is high and bouncy cuz previous owner removed all emissions , like the necessary bac so un regulated vaccum= bouncy idle.

 

Want to make sure I've got my terminology right. By primaries I mean the 3 plates that are in line, and the secondaries are the 2 on their own further away from the intake manifold.

 

no the two that are farther away im pretty sure are auxilaries helping the shift between primary opening up and then auxilaries lead to the secondaries in that order. primary is inline with secondaries. i could be wrong but i dont think so

primary is on top im sure of that hence the split in the dynamic chamber
throttle body mod gets rid of the fast idle cam and the auxilaries
secondaries are definately the two on the bottom

 

Here is a badly taken photo which shows the gap on the lower plates:

 

http://mazdarx7.iougs.com/intakeair.shtml

 

Thanks for the link, but not really sure what it's supposed to help me with. Are you saying that pic above is not how the throttle body should be?

 

""Want to make sure I've got my terminology right. By primaries I mean the 3 plates that are in line, and the secondaries are the 2 on their own further away from the intake manifold. ""


To clear up the notion that there is more than one primary plate as it is discussed in the link.

 

Right.

So, any idea about my problem?

 

Not sure how much it helps, but the two secondary throttle plates that are on the same plane as the primary throttle plate "begins" to open up when the primary plate has opened by approximately one fourth way.

I can't remember if you disabled your double throttle diaphragm in any way shape or form but if you didn't you could disconnect and plug up all associated vacuum hoses, soft and hard, to take it out of the equation.

 

Short answer, YES. those lower throttle places are supposed to be open @ idle...not really any way to get air w/o it.

According to the FSM/ Haynes manual there is a correct amount of gap that should exist between those plates and the TB wall. It also specifies how much the primary plate should be able to move before they start to open (ie. the should NOT start moving immediately when you start to move the primary plate)

The problem I have had is the BS "adjustment" method for manipulating the gap between the secondary plates and the TB. It says some crap about bending the rod that moves them, take a look at it, easier said than done!

Most people don't even worry about having the proper gap, and w/ a BAC or standalone w/ idle control, it doesn't really make sense to, but I've got a spare TB that I've modded, and I'd prefer to do it right since I'm in no rush.... only wish the adjusting procedure made more sense

 

Not the factory terminololgy. There is only one primary plate, and it is the one on a shaft by itself. There are two sets of secondaries; each has two plates on a common shaft. The set on the same plane as the primary are the #1 secondaries, and the set upstream of them (which has been removed in the intake pictured) are the #2 secondaries.

Your picture shows the #1 secondaries open slightly at idle, and they should not be. According to the FSM, (F2-35 thur 37), the secondaries should not begin to open until the primary is open about 15 deg, with a bore clearance of 0.04-0.07".

The air for idle comes through the hole in the primary plate, visible in your picture. The primary plate should have a bore clearance of 0.016-0.020" when the temperature is 77F. The manual does not specify, but implies the primary should be fully closed at idle when the engine is at temp.

That your secondaries are partly open at idle may be the source of your rough idle. The training manual specifies that the hole in the primary is there to provide a controlled amount of air "...for a smooth idle." The partly open secondaries may be providing too much volume/low velocity air and thus a rough idle.

 

Having the secondary throttle plates open like that will definitely cause a rough idle. The TPS takes its signal from the primary shaft only, so you are getting extra air that the TPS doesn't expect. If I push open the secondaries when idling it causes significant surging.

That will however keep the engine from flooding when starting. Up in the mountains I have to have someone to hold open the secondary plates when I start it.

 

yah he no longer has this problem as we resolved it in a different thread

 

To be honest it probably was a pretty big contributing factor, but I have a scarily stable idle at the moment, so it's all working out well. Or at least today it is...