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From the factory there is a sealant around the edge of the throttle plates to minimise clearance and air flow at idle. By polishing the throttle plates and bore you have removed the sealant and increased clearances. This may result in high and unstable idle and possibly throttle stickiness once you reinstall. It is a common occurence on rx7s and other Japanese cars of this era that were not designed with close tolerances in the throttle body.
People think they are cleaning carbon but the darker colour is a chemically resistant dry lubricant/sealant.
Tomei in Japan makes a paste called Tomei Throttle Coat which you can apply to the back edge of the throttle plates and the edges of the shaft to lubricate and seal. I know this is available in Australia but possibly not the US but other alternatives have been suggested on this forum.
I just ordered a tub for $71, this is after watching an Australian u-tube video showing how it is applied to close up gaps around the throttle plates.
I thought I trashed my throttle body, but this coating should do the trick!
Fabulous! Glad i could help and look forward to seeing how it goes. I found that video too and looks like a good way to apply it. For others, here is the video:
Hi again,
Here is a problem that you might have with manifold vacuum ports!
I got my parts back from my powder coating person, going over it I tried blowing thru the three vacuum ports on the side of the middle manifold.
All three ports were plugged up, not with powder coating but with carbon!
The port that has the right angle to it was a problem to open up.
I tried pushing a Stranded Copper Wire through the obstruction, but it did not go too far after the bend.
I had a thought, yeah, that's rare, so I tried spraying carb cleaner to the port, that didn't go well!
After running my eyeball with water from the kitchen sink, my thought changed.
Now, my bright idea that came next didn't involve squirting carb cleaner in my eye.
Okay, how about putting acetone into the port with a drop on the end of a toothpick, Sounds kinda okay.
Blocked vacuum ports
After adding many drops, I was able to dislodge the deposits and clear out the port.
This port seems to be how the blowby gasses and evap canister get pulled out and added to the intake mixture.
Getting rid of the blowby gasses is important, it is one of the problems with internal combustion engines.
They kind of blow-up if allowed to get built up.
So, try blowing through the two smaller ports, unless you have an automatic, then the large port comes into play.
I am surprised at how many blockages I have come across in my 88 GXL rebuild!
While tracing what all the ports on the dynamic chamber are for I found out these middle IM ports are just regular vacuum ports.
The middle port supplies vacuum to close the front secondary throttle plates on a cold start, this vacuum is closed off once the thermo valve on the throttle body reaches 140 degrees. Then the front secondary plates are held fully open by the spring tension in the diaphragm.
Every picture I took shows the right angle port has nothing hooked up to it!
Please, does anyone know what it goes too?
I just went through my 1988 Workshop Manual, pages 4A-56 & 57 to review how to correctly set the cam.
First, the diagrams for the cam adjusting screw and fast idle adjusting screw are pictured from the throttle body side! The cam is shown rotating in a counter-clockwise direction.
They show the 77degree "matching mark" and cam roller close to the edge of the cam, which is the edge where the roller separates from the cam when the engine reaches operating temperature.
The other cam marking is labeled 32 degrees. It makes sense for this mark to be further from where the roller separates when hot. I am assuming that the thermo wax would be pulled in further at this temperature.
If you go back and look at my picture you will notice a single mark to the left, then a double mark to the right. I have aligned the roller to the single mark.
With this setting the roller is on the far side of the cam from where it separates at operating temp.
I noticed a wear spot between the double mark on the cam, there is no mark where the single line is!
I tried screwing the cam adjusting screw in all the way to see if I could get the roller on the wear spot, not even close.
So, the range of travel for the adjusting screw has to be for the single mark. I wonder what the double mark is for.
The "Fast Idle Adjusting Screw" on the other side of the roller assembly is where you adjust the "Fast Idle Clearance".
It looks like some of the text on the page posted above went missing! You have to bend the tab for the secondary valve opening point, which doesn't look easy.
With the roller on the cam aligned with the mark, adjust this screw to change the primary throttle plate opening amount.
Plate to bore: .016 to .020 in.
Moving this screw does not change the cam alignment.
It appears that this section in the manual got mixed up in translation and pictures!
Hi again,
I am learning how to use a multi-meter to bench test my parts before installing them. I tested two TPS sensors and found that they both were within specs as per the workshop manual. But they were both different by 1k ohms on the high end, on the low end they were both lower than the 1k ohm spec. One was 500 ohms and the other was 450 ohms.
But this is normal, when I installed the one I picked, I noticed that the plunger was pushed in by the bracket on the primary throttle shaft quite a bit!
I retested the sensor and found out that I could set it to 1k ohms by adjusting the screw on the linkage by the sensor! So, the low readings while doing the bench tests were to be expected.
TPS installed and adjusted to 1k ohms
I will still do the recommended test and adjustment with the testing lights when it gets running again.
Thanks for the complement, I do have it in my will, going to my Nephew. If he wants it!
I have a lot still to do, now mostly the rotting unibody and the exterior.
Back to business.
Primary throttle valve
The throttle plates have a bevel on the edges going in opposite directions on each one. So, it is important that they are installed in the correct orientation!
On the primary plate the small hole goes towards the bottom, but you can install it with the bevel going in the wrong direction!
Viewed from the back side of the throttle body, the bottom with the hole in it will pivot towards you. The bevel will be on the other side allowing the valve to open like a door without sticking.
secondary throttle parts
The secondaries go together in the same way. Note that the 0.7 stamping on the plates go up and to the front of the throttle body.
I did not keep track of which one went in which bore! I polished the edges and now I see light coming through in various areas around the plates when they are closed.
I am not concerned with this, I did the best I could when installing them.
Throttle plates installed
Remember to put a little thread locker on the screws while installing them!
Primary throttle stop
Here is the set stud for the primary plate, I am going to adjust it so that the instant the throttle plate starts to open I see some light all around the plate.
If it is closed too much, I feel that you will need an extra degree of opening before the plate allows more air through.
So, I will back the stud out until I have just the minimum amount of closure ( no light showing around the plate ).
Then turn the stud in until the amount of light starts to increase. This can only be done with the throttle body removed from the car!
If anyone has more info on this setting, please let me know. I am doing what I consider reasonable.
Here I have pictures of the fast idle cam and follower.
First, I found the cam follower to be frozen with corrosion, using a razor blade and WD-40 it came loose and rotated once again.
I tested the thermo wax in boiling water and it ended up protruding a total of 8mm, so I assuming that it is working correctly.
With a few pieces of the primary throttle plate linkage in place I was able to determine if the fast idle cam was adjusted to the center of the cam follower.
You will see the contact point between the cam and follower, they need to be aligned very well!
I used a magnifying headset for a close look.
diaphragm delay valve
This is out of assembly order, but I have this picture of the delay valve.
Do not confuse this with the check valves used elsewhere on the engine.
The delay valve takes 9 to 15 seconds to release the vacuum on the diaphragm before the No.2 secondary throttle valve is fully closed.
The delay of 9 to 15 seconds is for a removed valve attached to a 1 meter long vacuum hose!
While tracing what all the ports on the dynamic chamber are for I found out these middle IM ports are just regular vacuum ports.
The middle port supplies vacuum to close the front secondary throttle plates on a cold start, this vacuum is closed off once the thermo valve on the throttle body reaches 140 degrees. Then the front secondary plates are held fully open by the spring tension in the diaphragm.
Every picture I took shows the right angle port has nothing hooked up to it!
Please, does anyone know what it goes too?
Hi again,
The reason that there are no pictures of what connects to the right angle vacuum nipple on the secondary intake manifold is that it was never used! It seems that it was blocked off at the factory.
I unblocked it just to put a vacuum cap on it! Oh well.
Hi everyone,
I went to apply my "Throttle Coat" to the plates when I noticed after blocking open the plates to get to the rims that the linkage was canted!
Canted linkage
Bushings that need to be thinner.
I sanded the metal bushing to about .005" thicker than where it fits into the linkage with the plastic bushing in place.
Then I thinned the plastic bushing so it was flush with the linkage. Giving me a little clearance between the plastic and metal bushings. I did not want them binding up.
Here is the alignment after thinning the parts.
Cleaned and given a coating of silicon grease. No binding that I can see.
The net effect is that I now have a few more degrees of opening at wide open throttle. More airflow, more power!
What do you think of this?
I also noticed that the connecting arm has a bit of play in it, maybe a turn of thin fishing line around each end will help?
Finally got around to applying the "Throttle Coat" to the valves.
First is a way to block the valves open to get the rims coated. leather block to hold open the throttle valves
This is the way to move the cam roller off of the fast idle cam. Pencil to move the fast idle cam and have the throttle plates fully closed
I applied three quickly coats, then open & close the plates a few times to spread the coating before it had a chance to dry. witness marks from fully closing the throttle valve while the coating is still wet
I am leaving the valves open overnight to let the coating dry.
There is also coating applied while the valves are fully closed. Using a long Q-tip. Came out a little messy but I do not have any light leakage around the valves now!
I will carefully use my finger to knock off any wayward bumps and ridges, then do the light leakage tests again.
If there are some areas that need another application of coating, I have plenty!
I used mineral sprits for clean-up, the coating is hard to remove when it is dry.
I added another coat to the throttle valves for a better seal. But in doing so I noticed that the primary throttle stop now has a large gap when the throttle plate is fully closed! I see about a sixteenth of an inch space!
I will go in and remove some of the coating by smoothing it out with acetone on a Q-tip. If I get it down to 1/32" gap then I will adjust the set screw to close the gap.
When I do this, I will need to readjust the fast idle setting and the TPS sensor to 1k ohms. Changing where the primary plate closes changes to other two settings.
Here are some pictures of the finished upper intake:
top left side right side front bottom
I replaced the stock nuts with either SS or brass acorn nuts to give it a different look. I added 8mm hose clamps to a number of the vacuum hoses that I am reusing, just to reassure me that they are a snug fit. I do not want to be chasing vacuum leaks down the road.
What do you think of it?
Hi guys and gals!
Earlier in my rebuild I removed the shaft O-rings without damaging them. I put a bunch of silicon grease on them overnight.
Wiped them off before re-installing them.
I read in another thread where air leaks past these shaft O-rings and causes idle issues!
Another thread stated that coating O-rings with ATF will swell the rings, is this for all 0-rings or only specific types like Nitrile?
What would it hurt if I applied ATF drops to the areas where the shafts enter the O-rings? Would it penetrate the ring enough the seal any air leaks?
If it does swell the rubber, how long would it last? Week? Month? Year?
From the factory there is a sealant around the edge of the throttle plates to minimise clearance and air flow at idle. By polishing the throttle plates and bore you have removed the sealant and increased clearances. This may result in high and unstable idle and possibly throttle stickiness once you reinstall. It is a common occurence on rx7s and other Japanese cars of this era that were not designed with close tolerances in the throttle body.
People think they are cleaning carbon but the darker colour is a chemically resistant dry lubricant/sealant.
Tomei in Japan makes a paste called Tomei Throttle Coat which you can apply to the back edge of the throttle plates and the edges of the shaft to lubricate and seal. I know this is available in Australia but possibly not the US but other alternatives have been suggested on this forum.
gonna have to disagree with you on that one, have cleaned thousands of throttle bodies on various cars including RX7 throttle bodies and never had any adverse effects from it, so i'm gonna have to say it's a myth that there ever was a sealant in there for the plates. it might not hurt but i also don't think this cures a problem that doesn't exist.
if it may in fact be a thing i feel it's one of those things that engineers put in that was an unnecessary step that serves next to no practical purpose. you should never need to set the plates closed so much that they bind up.
Last edited by notanymore; Mar 23, 2025 at 07:38 AM.
gonna have to disagree with you on that one, have cleaned thousands of throttle bodies on various cars including RX7 throttle bodies and never had any adverse effects from it, so i'm gonna have to say it's a myth that there ever was a sealant in there for the plates. it might not hurt but i also don't think this cures a problem that doesn't exist.
if it may in fact be a thing i feel it's one of those things that engineers put in that was an unnecessary step that serves next to no practical purpose. you should never need to set the plates closed so much that they bind up.
There was 100% sealant there from the factory and the same applies to most JDM cars from that era. The machining and casting back then was just not on the same level as modern manufacturing techniques, particularly compared with the modern aftermarket motorsport style throttle bodies.
You may not have had a problem from cleaning it off, but the lack of adverse effects does not make me wrong. And the whole point of the sealant is that the throttle plates seal without having to be closed so much that they bind. Small leaks will not present a noticeable issue if the amount of air is such that you still have enough adjustment in the idle air bleed to fine tune the base idle, but there are plenty of documented cases where people cannot get the idle low enough even with the adjustment screw fully in - or worse, there is leakage out of the throttle shaft under boost.
Hi guys and gals!
Earlier in my rebuild I removed the shaft O-rings without damaging them. I put a bunch of silicon grease on them overnight.
Wiped them off before re-installing them.
I read in another thread where air leaks past these shaft O-rings and causes idle issues!
Another thread stated that coating O-rings with ATF will swell the rings, is this for all 0-rings or only specific types like Nitrile?
What would it hurt if I applied ATF drops to the areas where the shafts enter the O-rings? Would it penetrate the ring enough the seal any air leaks?
If it does swell the rubber, how long would it last? Week? Month? Year?
Please let me know, it will be appreciated!
I found a thread about these quad ring seals (or star ring seals) for FD rx7's. They got their seals from Metric Seals Inc.
I enquired about their availability and they sent me a link for this particular seal.
I just received a package of ten for $36. Too bad, I could of used them while my throttle body was apart!
The size of these seals are listed as Q 10x2.5, the 10 is the I.D. the 2.5 is the thickness, since the cross section is square the O.D. is 15mm
There's actually a channel drilled into the throttle body to let the throttle shaft bypass some air, why it's there? i have no clue, i threaded mine and stuffed a screw into it. the hole is located underneath the base of the thermowax.
There's actually a channel drilled into the throttle body to let the throttle shaft bypass some air, why it's there? i have no clue, i threaded mine and stuffed a screw into it. the hole is located underneath the base of the thermowax.
Interesting, I will have to look into it when I rebuild my spare throttle body.
How everything works together with the throttle body is a mystery that only the original Mazda engineers understood.
What am I looking at, and what does it do?
Why is it necessary and how does it work?
When it doesn't work how do I fix it?
Rebuilding the throttle body seems straight forward compared to rebuilding a carburetor, they were very fussy about how they were cleaned and setup.
The field service manual covers most of the settings needed for the throttle body to work.
The only thing I am concerned with is the extra air drawn into the intake manifold due to the wear of the quad seals on the throttle shafts and any spaces around the throttle plates.
If the extra air is minor, it can be adjusted for by the idle adjusting screw at the top of the throttle body.
If the wear is too much, then the seals need to be either swelled with ATF or replaced. Any space around the throttle plates needs to be sealed closed.
Once you know what to look for it is pretty simple, the difficult part is to remove the throttle body to check the clearances!
That being said, if you have disassembled the intake, go through it thoroughly and double check all the settings.
there's plenty more places for air to leak in the system that many folks neglect, i have never had to actually rebuild a throttle body to get a car to idle down properly.
there's plenty more places for air to leak in the system that many folks neglect, i have never had to actually rebuild a throttle body to get a car to idle down properly.
It's the little things that count.
Can you please give us some of the more common occurrences of vacuum leaks on these engines?
And maybe a few of hard to detect leaks?
My areas of concern are with leaks from only the throttle body itself.
Hello again,
In another thread I explained how the double throttle plate system works. The thermo valve regulates the vacuum that controls the amount of movement of the diaphragm. Under 140 degrees allows vacuum to be applied and the #2 throttle plate to fully close, once the coolant temperature reaches 140 degrees the vacuum is blocked completely and the spring in the diaphragm pushes the throttle plate fully open.
I just received another thremo valve for my spare throttle body, when I tested it there was two problems with it. When I blew air into one of the nipples and blocked off the other there was a small air leak where the brass is crimped to the plastic piece. I tried gently squeezing the crimped edge, but it just moved where the leak was! So, I applied a bead of crazy glue around the crimped area, let it cure overnight and then re-test it the next day. The leak was still there, so I added another bead of glue. This did the trick and the leak was finally sealed.
The other problem was that the plunger that moves to block off the vacuum was sticking so that the temperature where it finally blocked off the vacuum was 190 degrees! After sitting for 35 years unused it is to be expected. I squirted some WD-40 into the nipples and the area where the cap goes and let it sit overnight. On the re-test, the closing temp came down to 185 degrees, So I tried shocking the plunger by putting it into boiling water for a few minutes then running it under cold water. I did this about five times and applied more WD-40. The next day it tested 150 degrees, so it finally freed up most of the way. Enough to be confident to use it again.
Here is my technical laboratory testing apparatus to verify my theory: Open end with some WD40 in it, once it opens the oil will flow down inside the plunger.
If your valve in not working correctly, give this a try.
I would squirt some WD-40 up into the nipples when the valve is installed on the throttle body for maintenance every few years.
Last edited by gsmithrx7; Apr 19, 2025 at 05:07 PM.
Reason: add a comment
Thank you for posting the thread and all of the responses, I will be needing this soon. There are some other threads on here too that will guide me along as well. I am a bit aprehensive to do this because I have succesfully rebuilt a weed eater carb in my day. .... that's it.
I have taken this rebuild over the winter, now spring is upon us and time to install the rebuilt engine.
The disassembly of my frozen throttle body went pretty smoothly, refinishing all the pieces took some time but turned out okay.
Now I have to remove some of the throttle coating to get the throttle plates to seat without any light showing around them. This is important to be able to adjust all the other throttle body adjustments to specifications as per the FSM.
All these adjustments are fairly easy once the throttle plates are fully sealed at hot idle. Otherwise, you will be adjusting the settings to a throttle plate leakage which affects all the FSM settings!
So, make sure you have a good seal around the X-rings on all the throttle shafts, either replace them all or try swelling them with ATF!
Seal any gaps around the throttle plates with the coating described above, just enough to close any gaps, the less the better.
Adjust all the throttle body adjustments as best that you can to the FSM, repeat as many times as it takes for the adjustments to be steady.
I believe that if you take the time and verify that the above recommendations are good, you can be assured that the throttle body adjustments are not a problem with how your engine is running!
Oh well.
.... that's it.