Intake Leak Testing, and the Throttle Body Shaft Seal Replacement

Last Modified: 2014-10-30

Update: 2006 07 15
Added a bunch of little updates, particularly on where to look for leaks, and things to look for if you have an aftermarket sheet metal intake of some sort. Fixed some typos.

Update: 2006 05 11
Philip Spigelmire - Sent me updates for the 1990 throttle bodies, that are apparently different than the rest of the years. One of the seals is smaller.
Read the whole thing first, but right at the end, I've added a section just for the 1990 model year. To his credit, he sent me this info in February of 2004, but I just found it today.

Update: 2003 12 11
Added a few suggestions and corrections.

Update: 2004 06 22 (from Alex)
FYI, NAPA doesn't seem to be able to get these seals anymore and Pep Boys, while having the number listing, can't order it and told me "I think it has been discontinued."

I checked Kamandirect and they list the seal as unavailable.

I finally found a place that can order it from the manufacturer and should have them to me in a week. The reason I am even telling you this is cause it is a national company, Motion Industries, with retail stores all over the country and Canada:

They want $5 per seal + shipping and they will do whatever shipping you are willing to pay for.

Let me start off by saying, that while this is a fairly simple process, it is also fairly detailed, and should not be attempted with a monkey wrench and a pair of pliers. I also take NO responsibility for anything you may break, damage or destroy, or for any warranty you may or may not affect on the vehicle in question.

This VFAQ was written after the fact, so you should at least read the entire thing once, prior to attempting it. It only took about an hour to do the job, pictures included, but YMMV.

That all being said, are we ready?

Many thanks to Steve Kinnaird, aka Captain Torque Steer of the Kinnaird Modelling Academy... as he has provided the car for the pictures, as well as the lovely hand modelling.

Thanks also go out to the members of Club DSM Canada for hosting this VFAQ for us, and to Tom Stangl for the main index.


Part One, deals with how to test for a leak, if you have not already done so. You may have many leaks, in addition to your shaft seals. Most people, find many leaks, and it simply becomes a question of "correct, and re-test".

Simply put, you have to plug the intake of the turbo, and then pressurize the rest of the system... listening for leaks.

As you can see here, we have used a bit of rad hose, a similar diameter metal can, and a couple of clamps to seal the inlet to the turbo. (clamp the hose onto the turbo inlet, and then clamp the hose around the can to make it into a big plug)

Rob Strelecki has mentioned, that Home Depot carries a nice coupler, just about the right size for this, or any coupling process. FERNCO #1056-22 -- comes with coupling and two clamps.

In recent tests, on my own car (20G), I have found that a Becks beer bottle fits nicely into the silicone coupling on the turbo inlet.

After that, tee into one of the vacuum/pressure lines on the engine, and pump in some air.

I now prefer to tee into the BOV line, running from the intake to the BOV. This ensures that the intake is getting max air (it's a larger nipper) and that the BOV is seeing the pressure as well, so that it will stay closed. (just like when the car has boost)

As you can see at the end of the purple hose that our local test monkey is holding, we have tee'd into the BOV line.

This is an easy line to get at, and functions well for our purposes.

the other end of the hose is going to a manual air trigger, which is in turn being fed by an air compressor. Be careful where the regulator on your air compressor is set to... you wouldn't want to pump 100 psi into your intake. We set it for 25psi when flowing.

Recently, I have started using a 0-30psi inline air regulator. These are NOT hard to get, most stores that either sell air tools, or painting supplies, have them, for use directly on the bottom of paint or powdercoating guns. Mine came with a little gauge on it as well, so I can see exactly how much pressure I am putting it, how the intake is responding, etc, right in the engine bay. Well worth the investment.

That's it... listen, feel, look, for leaks. You'll likely have a few. Have a buddy watch your aftermarket pressure gauge in the car, to see how much pressure you can hold, and this will help gauge how your repairs are coming along, as you eliminate the leaks.

For example, if you can see 20psi under the hood at the regulator, but only 17 at the dash, then you're losing air. The closer you can get, the better.

It is natural, that a small amount will leak out the tailpipe, but cap other things, like the crankcase vents, if you can.

Sheet Metal Intakes

These are very popular these days, some also installing them with phenolic spacers, to reduce heat transfer from the head.

Make sure, if you have a spacer, that the bolts and stud nuts are very tight. Phenolic is hard stuff, but, not as hard as aluminum. I have noticed bolts and nuts working loose. At this point, I don't know if it's heat cycling, shrinkage of the phenolic, or just vibration. In any case, I've tightened them up "good", and added locknuts to the studs.

One brand of intake in particular, that is VERY popular, has been known to develop cracks in the welds. Look for leaks, around the joints and welds. (I had 5 in mine, and have repaired welds on two others now)

The manufacturer has specified that if you contact him, he will repair the cracks. But, if you don't have the time to wait for that, consider other options. On mine (a very early beta product), three of the leaks were welding fissures, or, defects in the weld, that were acting as vent points.

I already had the intake on the car, and it was also polished and powder clear-coated, so I didn't want to remove it and start welding again. I mixed up some 5 minute Epoxy, and coated the leaks, after cleaning the spot thoroughly. They now, no longer leak at all. The epoxy has excellent bonding properties, and my intake never gets very hot.

Another member also suggested "sand it, and apply some JB weld", but I don't know how well JB Weld works with aluminum. (no experience with it)

The best option, of course, is to have the manufacturer repair the intake, under warranty. I've heard, that their newer ones, come with extra structural supports, to try and prevent the cracking.

It would be nice if they would also pressure test them, but I don't think they're setup for that. You might want to try, before bolting everything back up again.

Throttle Body Shaft Seal Leak

This is likely why you're here reading this, so if you're still in the mood to double check yours, listen around the throttle body. It's in the circle below, roughly speaking.

Please excuse the fuzzy tail, the cat just couldn't avoid helping us. Who said we couldn't ever get a pussy on the hood...

As you provide pressure into the system, you will hear it leaking from this general area. If you then manually rotate the throttle plate (or have the buddy in the car step on and off the gas) you will hear the sound changing. This is the leak around the shaft seals.

The problem with these things, is that they're simple rubber seals, bonded to a metal ring. Over time, the rubber they used, gets tired from the heat, oil, etc, that it's exposed to, and just goes rock hard. As you'll see later on, the residue it leaves on the shaft as it's breaking down is terrible to try and remove. The rubber is now like hard plastic, as you will see if you go on to dissect it. They were likely not ever even thought of as much of a problem in design, as they're definitely a long-term wear item that most customers would never notice.

So, assuming you have purchased a pair of 14mm x 10mm x 4mm (or 3mm) shaft seals, and are ready to proceed, let's get going.

As an aside, Craig Berndt did some looking and has found a place where one can obtain the seals. I was purchasing them from a local supplier in my area, but wasn't sure whose make they were, only that they worked. Craig says that they are available from Chicago Rawhide, part # 3930 CR 10x14x3 HM4 R. He also has suggested using as a source to purchase them.

Steve Piette also emailed to say that NAPA can get them as well, using the above CR part number.

John Novo provided this source, and these images of the ones he bought from them.

I cannot speak for any other sources, or the seals from this location, as I have not tried them, but people assure me that they are the same.

Parts Removal

You will need to get at the TB.

Therefore, remove things that are in the way, including the upper intercooler pipe, and possibly the battery, depending on the year of your car, and your patience with getting tools under the TB elbow.

Disconnect the ISC (idle speed controller) motor electrical connection, under the TB, on the passenger side of the car. It's a multi-pin plug, and has a little plastic spring release, so don't just yank it off.

Remove the wire to the "throttle plate closed" sensor. This is located on the rear side of the TB, and is ONLY on the 1G cars.

Remove the two coolant hoses going into the lower side of the TB. Make note of which one is which, so that you can clearly connect up the correct ones again when finished.

On the top front side of the TB, is the TPS (throttle position sensor) and it's connector. This one is a bit of a bugger to get off, as the clip spring holding it on is complex to get off without breaking. Have a look around it's base, and figure out which side of the spring clip to pry with a screwdriver to get it loose. Once loose, the plug comes off.

Do not remove the TPS at this time... just the wire connection to it.

Label and then remove the hoses going to the top of the throttle body.

Reach behind the TB, and find the throttle cable. You will have to un-hook this cable from the throttle plate wheel. The easiest way to do this, is to crank the throttle plate open with your hand, and then fiddle with the cable to get it rotated around and out. It links in, like the cable on the end of a bicycle hand-brake.

If you're having problems with it, have a look at some of the pics later on, to get an idea of what you're dealing with.

It's the thing to the left here...



Unbolt the four bolts holding on both the TB Elbow and the TB itself, if you have not already done so to remove the UpperIC pipe.

Take great care in removing both items, so as not to damage the gaskets. If damaged, they should be purchased and replaced, or replacement ones cut from gasket material.

Once off, clean it up, and move to the workbench.


First things first, and very importantly.

Get a pad of paper and a pen out, and keep them handy. A good part of this procedure is simply re-assembling what you have taken apart. You will be much better off, if you make a few notes as you go, as to which way things go, and which way they came off. Trust me.

Mark the TPS and the housing next to it, in SEVERAL places around the outside of it. (use a scribe or similar permanent marking device)

This is to ensure that you can get it back EXACTLY where it was on the TB, when re-assembling it.

Without these markings, it will be very hard to get it right on your own, and you may end up having a lot of problems. (link below, to help if you screw it up)

Move any hoses and wiring harnesses out of the way, but you shouldn't have to disconnect anything more.

As you can see, we did it while the TB was still on the car the first time, but I would now recommend marking it up after you take the TB off the car, and in that way, you can mark it in MULTIPLE places around the housing, to ensure that it gets back on there EXACTLY as it came off.

It's now safe to unbolt the two screws that hold the TPS sensor on the TB. Set both and and the sensor aside.

Gently remove the nut from the end of the TB shaft, that is hidden under the TPS. Put the nut and washer(s) in a safe place, and remove the sensor arm (the little metal piece that the nut is holding on). It has a marking on it to indicate which way is bottom, but make a note of it.

Some years also have a little washer under this piece, so look carefully. If all is off, you should now be able to see one of the dreaded seals, first hand! (patience, leave it alone for now)

The other side, is a little more complex, as it has the throttle cable connection, and the spring return for the TB.

Make note of which way everything is on there (like the picture) and remove the nut and washer(s).

Pay VERY CLOSE attention to the springs, and where they hook on. There are actually two of them, one inside the other. Both have tension in them, and can bite. Make note of how they hook up, as you will have to re-assemble it again afterwards.

Suggestion: put a white stripe of whiteout or shop marker across the springs, in one or more spot. Then, when you go to rewind the springs, it will help you get the correct tension wound back onto it.


They are wound up, almost two complete revolutions, as you will see when you start to slide the end off the shaft, and it has a chance to spin... but you must take them off.

Slide the spring assembly off, and save any washers or bushings that are on the shaft under it.

Notepad and marker time again... make some notes, and then label your actual throttle plate, as to which side is which, and which way up it goes. Also, make note of which way it tips when it opens. This will help you when re-assembling, to make sure it's opening identically again.

The screws are screwed in, from the throttle bode elbow side of things, remember this when re-assembling.

Tough part now... removing these damn screws.

We used a larger Phillips screwdriver, as you can see. It had a nice hardened tip, that fit the screws nicely. Pick through your tools, and find the best match for the screws.

Be careful, the screws are in there very tightly, but they are quite possible to unscrew and remove, if you're careful. It has also been observed that they are likely peened (pounded) on the backside to prevent them from coming loose, which makes it that much harder when you want to remove them.

One suggestion made by a member out there... was to grind off the backside of the peened over screws, just to make it easier to remove without damaging threads. (just use some locktite when you put them back)

So, remove them.

(the link at the end, has some more good advice on removing them)

The throttle plate screws are pretty hard to get out without screwing them up.
Some people ended up having to drill one of them out. In case a replacement is needed, the threaded holes in the throttle shaft are 4mm x .75 thread. Some used flathead screws with 6mm thread length to replace the stock screws, and used red locktite. They also cleaned up the threads in the shaft with a 4mm x .75 tap, because it appears the stock screws are peened to hold them in place, so they tear up the threads a little bit when they are removed.

You should then be able to rather easily rotate the shaft, and slide the throttle plate out of it's slit in the shaft.
Once the plate is out, you will be able to easily slide the shaft cleanly out of the housing. Note from the picture above, which end is which, but it would be pretty hard to mix them up.

Clean the shaft, with whatever you have available, that is NON-Abrasive. ie: do not use sandpaper, or emery cloth.

The shaft must remain smooth and clean, but we need to get any remains of the seal off of the shaft, prior to re-assembly. Some lacquer thinner or acetone may be your best bet to get any and all residue off the shaft, particularly where the seals ride on the shaft.

To now finally get the old seal out of each end, put the blunt tip of a screwdriver, under the metal lip of the old seal and pry it out. It should just pop right out of the end of the housing.

This metal ring you just popped out, is part of the OLD style shaft seal, and is no longer needed. Get rid of it. It will not be going back in.

The new proper seals, have a metal interior for strength, but are completely encased in rubber, and are a complete replacement for the stock piece, which was rubber bonded to one side of a metal ring.  (this is not a half-assed o-ring insertion solution)

Once you clean out any and all residue in there, the ends on both sides should look like the picture here.

If there is any rubber or plastic residue, just clean it out completely.


Time to start putting it back together.

Grab some silicone dielectric grease or something similar, to lubricate the seals and ends of the shaft with. I recommend that you use silicone dielectric grease, because it is not petroleum based, and will therefore not tend to harden the new seals prematurely.

When looking at the seals, you will see that they have a solid side, and an "open" side. The open side should be installed facing inwards on the TB, on both sides.

Goop them up good, and don't worry if you leave a little on the bore of the TB when installing them... it will only help.

Gently press the gooped up seal, into the outer bore. The solid or closed side should be facing out towards you. Repeat for the other side of the TB.

Leave a little extra goop on the bore behind the seal, to assist in the easy installation of the shaft, and to let any extra settle into the back side of the seal.

At this point you should carefully slide the cleaned and polished shaft back into it's place. Take care as to not disturb the seals you have put in there, but if the shaft is clean, and maybe even a bit gooped with silicone dielectric it should slide into place nicely.

Feel free to play with it's rotation at this point, and get the feel for how clean and smooth it is now rotating within the new seals.

Get the screw holes pointing in the correct direction up, and re-insert the throttle plate, per your own notes.

With the screws still loose, test the rotation of the shaft, to ensure that you have correctly re-assembled it per your notes.

It should be opening the same way it was before, and without any interference from the sides of the TB.

As well, if you hold it up to the light, it should made a good seal with the sides, when the plate is closed.

Tighten both screws well, when you're happy with them. Really well... we don't want them coming loose, 'cuz guess where they will end up. You may want to use some Loc-Tite Blue on the screws, or something similar, to ensure that they never move again.

I also want to add, that this last picture is deceptive, as to the rotational position of the throttle plate, and the arrows on the plate. If you look at yours, prior to disassembly, and compare it with this picture, you will see that it cannot rotate as shown in the picture. This is because when I did it the first time, I didn't follow my own notes, and installed it from the wrong side.

Follow your notes, and you won't have to take it apart again, like I did. (I didn't think to take another picture!)

Or, as recently suggested to me... there are factory markings on the throttle plate. These should be on the upper half of the plate, and facing outward towards the throttle body elbow side.

The Rest

The rest, is pretty much the reverse of disassembly.

So, put things back on, in the reverse to how you removed them.

The spring is two full winds for both, and is a bit of a pain, but quite possible.

As you reach each point (after the spring in particular) test the operation of the TB. It should snap shut as it did when you removed it.

Get the TPS back on there, according to your many marks you made on the housing. Be extremely precise about this, as it's critical to operation... more so even on the 2G cars, as their Throttle Plate Closed sensor is part of the TPS.

Bolt the sucker back on the intake, with new gaskets if available. The manual calls for 14 ft-lbs of torque on the main 4 bolts that hold the TB on the car. You may find it easier to put the ISC motor connector and coolant hoses back on, prior to bolting up the upper IC pipe again. Throttle cable and TPClosed Sensor (1G) similarly.

Again, the rest is just the reverse... find everything you took off, and put it back on again in the correct place.


New gaskets should be used on both sides of the throttle body.

Even with proper gasket prep goo/spray, I personally still found mine to be a source of another leak, around the gaskets. (it may just be mine, I have a few oddball parts in there)

So, it's up to you, but I have now replaced my gaskets with a very thin layer of RTV Ultra Copper (high temp) silicone on both sides. Applied sparingly and spread with a long Q-tip type applicator. And... it doesn't leak any more.


Now, test for leaks, and you will find that you have none in that area any more. Now you can focus on the other ones...

The last thought I have, is one of caution. As mentioned, during reassembly, make sure the throttle plate is operating, and returning to the closed position firmly, and on it's own. The spring is strong, but if you don't get them both back wound up twice again, or your plate is mis-aligned, you could run into your throttle plate sticking open, and NO ONE wants that to ever happen.

Test it, check it, and double check it after you have tightened everything up on the car.


Charles Monk, did a fantastic job on another VFAQ, which included the previous method of using o-rings to fix up the old seals, rather than just replacing the seals entirely. It's worth giving his entire VFAQ a read, to get at least one other person's perspective on the removal and disassembly of the TB.

He also has a good VFAQ on re-adjusting your TPS, just in case you didn't quite mark it well enough during disassembly and now are having any idle or deceleration issues.

Thanks to James McElfresh for some good suggestions of corrections and things to add!


Any suggestions, questions, upgrades, improvements? Email them please.

1990 Model Year DSMs

...are a bit different.

There are two different sizes. One is the same as above, and the second one is 8mmx12mmx3mm.
There is a seal this size available from Chicago Rawhide as part# 3030.
A 1990 throttle body, has quite a few differences that were noticed. The ISC motor is different, and there is no connector on the TPS sensor or the ISC motor. Also the throttle body itself is one cast piece instead of two bolted together.
The VFAQ says to use replacement screws that are 4mm x .75 with a 6mm thread length. Philip picked up some M4 x .7 with 6mm length and they were a little short. He then picked up some M4 x .7 with 10mm length and those look to be an exact match with just enough out the back to peen them in like the stockers. Not sure if the 90 shaft is thicker.
Shaft with small seal.