aem1948

I really need help. This issue may have been covered before but cant find anything. I recently purchase a 99 miata, got a P0402 so looked it up and performed clean of the TB and intake. I used TB cleaner and cleaned it a little to good. Removed the soft seal around the Butterfly valve. Idles at 1500 to 1700 now. Have called around for a replacement but doesn't appear to exist. Don't want to buy a TB if can avoid it. Does anyone know where i can get a replacement seal or how to fabricate one.

18psi

iTrader: (76)

Welcome.
You'll probably need to replace the tb. Should be under 100 at a scrap yard.

DammitBeavis

There is a soft seal around the butterfly valve?

aem1948

Just now checking posts. 18Psi thanks for response, will start looking for replacement TB. Dammitbeavis, understand soft seal around butter valve I washed mine off with TB cleaner. Looking for replacement seal or how to fabricate one. thanks for reply.

DammitBeavis

I understand what you are saying, but I've cleaned mine so that all that was left was shiny aluminum. I've never seen any sort of seal around the throttle plate nor a place where one belonged. It certainly wouldn't need a seal there anyway. Are you sure you didn't just wash away the ring of oily carbon that builds up around the edges?

Edit: Just remove the rubber plug from the idle air bypass screw on top of the TB and tighten it up a little to get your idle back under control. There is also a stop screw on the TB pulley if the bypass screw doesn't have the range you need. I can't find any data that suggests there's anything in there but a smooth aluminum tunnel.

aem1948

There was a seal (was stronger than oil/carbon) prior to cleaning. didn't realize until to late. It may be a change for the NB. Have been reading up on the TEN and Gnd requiirement. Will try the bypass screw in hopes it will fix issue. Will be over weekend due to work schedule. Tks

DammitBeavis

Can somebody take pics of said 'seal'? I find it hard to believe an engineer would put any sort of lip at the edge of a butterfly valve on a throttle body considering that they don't close all the way in the first place. I have never seen this on any other TB, and I've seen quite a few.

aem1948

This is the only site that had a picture, several Google searches threads talked about the seal. http://www.cardomain.com/ride/210139...a-mx-5/page-12

DammitBeavis

Fascinating. I went out and grabbed one of my '99 TB's in the garage and snapped some pics:

Stamping: https://picasaweb.google.com/lh/phot...eat=directlink

Dirty: https://picasaweb.google.com/lh/phot...eat=directlink

Clean: https://picasaweb.google.com/lh/phot...eat=directlink

Edit: Not sure why I can't attach images, but whatever....

DammitBeavis

Upon further reflection, that image says it's from a 1990 MX-5, and looks completely different from a '99.

chicksdigmiatas

iTrader: (11)

I guess all of our seals have been sucked into our engine then. Mine never had one.

Faeflora

iTrader: (2)

So what is the final answer on this? I have never heard of such a thing.

What about yiur idle scew? Did that fix it?

DammitBeavis

LOL, it's on our own ******* forum.
https://www.miataturbo.net/general-miata-chat-9/throttle-plate-seal-47460/

If this is really on a '99 then you have the wrong TB.

In summary, don't worry about it, just reset your idle with the screw and/or throttle stop. Just don't set the throttle stop so that the plate can jam in the bore.

Faeflora

iTrader: (2)

What a great name you have Cocktimus. Huzzah!

aem1948

Thanks for replys. I'll be working on the idle ajustment over the weekend.

aem1948

I started working on getting idle set. I have a scangaugeII and had it hooked up to compare to my dash tach. had car ready to go and was jumping the TEN and SGND. My DC has capability of pinning the KLN, TEN, +B, SGND FSC, and the FAB, IG-, GND, F/P. I was pinning the TEN and SGND when the car stalled. Disconnected jumper, and tryed restarting car but does not start, fuel pump work and engine turns over. I don't think I touched any other connection when tryed to jump the TEN and SGND but wouldnot swear to it. Does anyone have any ideas on what I may have shorted/done.

aem1948

Disreguard previous post. Started researching and per web found 15a fuse blown in fuse box under dash. I was using wrong GND, every thing i had found to date showed TEN to SGND on left of DC box. Will try again using TEN and GND on lower part of DC box.

aem1948

To all was successful in setting idle. Jumped TEN to correct GND. the butterfly was open quite a bit since it took over 3 full turn to start getting idle to start dropping. ended up having to turn screw until it bottomed out, backed screw out half turn but could only get rpm to approx 1100. got fed up and just pulled jumper and low-and-behold had tach drop to 839-850rpm. Took for a drive and upon stop idle holds at approx 1100 and after a few drop to 850rpm. So i guess i got it right. Now just have to get car toshop to have Cat and O2 sensors checked to pin-point P0420 problem.
thanks for assist.

Joe Perez

iTrader: (8)

Sounds like this problem is revolved, but in the interest of cleaning up some loose ends...
The "seal" which is being referred to, between the throttle plate (the "butterfly") and the throttle body casting is not a seal in the sense that most people are probably thinking here; it's not an O-ring or a gasket or any discrete physical device. It's merely a surface treatment which is applied to the parts in the area where the plate meets the housing.

The thread that DammitBeavis linked to shows a picture of the area in question. You can see here a sort of grey coating all around the throttle plate:

aem1948

Joe thanks for info. By any chance do you know of someway to restore the "seal". Or is it now a matter of idle screw adjustment?