12V Throttle Body Gasket
03-13-2003, 10:30 AM
#1
AudiWorld Super User
Thread Starter
12V Throttle Body Gasket
<center><img src="http://pictureposter.audiworld.com/711/tbgasketfix.jpg"></center><p>originally posted by 'URs4':
I stumbled upon this a few months ago chasing an intermittent miss at idle and wandering idle.
Spent over a week chasing the problem, replacing many parts and swapping several throttle bodies out only to discover that it was a gasket issue. Seems any/all gaskets with over 20k miles on the clock have hardened and shrunk to a greater/lesser degree due to heat. When it does this it's starts allowing unmetered air into the TB and subsequently, the engine. And while the engine has management systems to correct for this it's not sensitive enough to pick up smaller amounts of unmetered air. Sure it does it's job if there's a catastrophic leak or gasket failure but it's dismally poor at sensing smaller amounts of unmetered air. Any Audi w/20K+ miles will allow the TB to separate from the plenum when removed from car just by turning the TB downward. Falls right off! That is NOT a good seal! Bear in mind that 15-18" of vacuum is as crazy about getting positive pressure into a sealed container as a positive pressure is about getting out of a sealed container. And it's indiscriminate about where it comes from... the path of least resistence will always be vacuum or positive pressure's first choice to relieve itself.
In light of that, fuel/air ratios are influenced/affected, particularly at idle when most vacuum is developed. Subtle irratic idle issues occur and people spend gobs of time, boatloads of money diagnosing and replacing things that aren't necessarily faulty or bad. And some of these leaks are so subtle that the cars sensor systems can't pick it up and therefore the VAG is useless as it only scans those sensors memory. I have one throttle body now that was diagnosed bad at the Audi dealer and was given back to the customer after it was replaced out of warranty. Of course they also installed a new TB gasket and guess what? Yep, car worked fine. But guess what else? There's not a thing in the world wrong with this throttle body or for that matter with the gasket that a little "ounce of prevention" won't cure. After doing this little mod that throttle body and gasket are perfect in every way... even better than when new.
The trick:
Remove the plenum from the throttle body taking care not to lose the TB's rubber stud bushings located at the left/right side (when viewed from the top). They fall out easily and are a bear to find sometimes. You don't have to take the plenum out... just push it away from the throttle body far enough to remove the thick rubber gasket around the TB's air horn (inlet)... the one that's supposed to seal the mating surfaces of the TB/intake plenum.
Now take a piece of everyday RJ11 phone cord. Everybody's got plenty of that lying around. I used white in the pic for photo contrast but any color works fine. Cut a small length of the RJ11 to 11" long (11 1/16" is better but no longer!). "RJ11 to 11" (easy to remember). You can cut it straight or you can cut the ends in a mitred fashion like I've done in the pic to make the 'seam' all but disappear. My seam is visible in the pic and not hid in the far right side and it's almost visually imperceptible.
Once you've cut the cord to length, it will slide easily into the inner groove, between the seal sections for the TB and the plenum. Use a small, dull, plastic punch to fully seat the RJ11 into the recess. I use a Bic Stic pen body with the cartridge removed and a small notch ground in the end using a Dremel and an 1/8" drill bit.
Now seat the gasket back on the throttle body. It'll be a lot tighter this time. Place some clean engine oil on the small tapered section of the gasket O.D. where it goes into the plenum. Then place the plenum back over the TB gasket. Note: It will be a lot harder to get on as it's now sealed the way it should have always been. Bolt everything back up and you're done.
I originally did these with 14ga wire and later with o-rings I purchased for specifically this mod. But the RJ11 works so much better and is abundant as well as offering the additional benefit of it's sealing area spread out over a far greater area.
Under the plenum area can be a difficult location to work in but nothing major.
When I send a converted throttle body out I always include one of these in the package. Funny how many have just tossed it thinking it was just clutter/trash in the box. I now tellem what it's for. Oops!
Hope this may prove helpful to someone. But everyone with 20K miles could benefit. And the price is certainly right!
I stumbled upon this a few months ago chasing an intermittent miss at idle and wandering idle.
Spent over a week chasing the problem, replacing many parts and swapping several throttle bodies out only to discover that it was a gasket issue. Seems any/all gaskets with over 20k miles on the clock have hardened and shrunk to a greater/lesser degree due to heat. When it does this it's starts allowing unmetered air into the TB and subsequently, the engine. And while the engine has management systems to correct for this it's not sensitive enough to pick up smaller amounts of unmetered air. Sure it does it's job if there's a catastrophic leak or gasket failure but it's dismally poor at sensing smaller amounts of unmetered air. Any Audi w/20K+ miles will allow the TB to separate from the plenum when removed from car just by turning the TB downward. Falls right off! That is NOT a good seal! Bear in mind that 15-18" of vacuum is as crazy about getting positive pressure into a sealed container as a positive pressure is about getting out of a sealed container. And it's indiscriminate about where it comes from... the path of least resistence will always be vacuum or positive pressure's first choice to relieve itself.
In light of that, fuel/air ratios are influenced/affected, particularly at idle when most vacuum is developed. Subtle irratic idle issues occur and people spend gobs of time, boatloads of money diagnosing and replacing things that aren't necessarily faulty or bad. And some of these leaks are so subtle that the cars sensor systems can't pick it up and therefore the VAG is useless as it only scans those sensors memory. I have one throttle body now that was diagnosed bad at the Audi dealer and was given back to the customer after it was replaced out of warranty. Of course they also installed a new TB gasket and guess what? Yep, car worked fine. But guess what else? There's not a thing in the world wrong with this throttle body or for that matter with the gasket that a little "ounce of prevention" won't cure. After doing this little mod that throttle body and gasket are perfect in every way... even better than when new.
The trick:
Remove the plenum from the throttle body taking care not to lose the TB's rubber stud bushings located at the left/right side (when viewed from the top). They fall out easily and are a bear to find sometimes. You don't have to take the plenum out... just push it away from the throttle body far enough to remove the thick rubber gasket around the TB's air horn (inlet)... the one that's supposed to seal the mating surfaces of the TB/intake plenum.
Now take a piece of everyday RJ11 phone cord. Everybody's got plenty of that lying around. I used white in the pic for photo contrast but any color works fine. Cut a small length of the RJ11 to 11" long (11 1/16" is better but no longer!). "RJ11 to 11" (easy to remember). You can cut it straight or you can cut the ends in a mitred fashion like I've done in the pic to make the 'seam' all but disappear. My seam is visible in the pic and not hid in the far right side and it's almost visually imperceptible.
Once you've cut the cord to length, it will slide easily into the inner groove, between the seal sections for the TB and the plenum. Use a small, dull, plastic punch to fully seat the RJ11 into the recess. I use a Bic Stic pen body with the cartridge removed and a small notch ground in the end using a Dremel and an 1/8" drill bit.
Now seat the gasket back on the throttle body. It'll be a lot tighter this time. Place some clean engine oil on the small tapered section of the gasket O.D. where it goes into the plenum. Then place the plenum back over the TB gasket. Note: It will be a lot harder to get on as it's now sealed the way it should have always been. Bolt everything back up and you're done.
I originally did these with 14ga wire and later with o-rings I purchased for specifically this mod. But the RJ11 works so much better and is abundant as well as offering the additional benefit of it's sealing area spread out over a far greater area.
Under the plenum area can be a difficult location to work in but nothing major.
When I send a converted throttle body out I always include one of these in the package. Funny how many have just tossed it thinking it was just clutter/trash in the box. I now tellem what it's for. Oops!
Hope this may prove helpful to someone. But everyone with 20K miles could benefit. And the price is certainly right!
03-13-2003, 02:00 PM
#4
Until and if the heat goes much above 275F it's only ill-affect is a little jacket shrinkage...
That is to say the inner, individual wire insulators and the outer jacket will shrink approx 1% along it's entire length. The cool thing about this reaction is that it also then conforms better and takes on the shape of it's surrounding retaining sleeve, ie; the inner folds of the TB gasket.
The RJ11 outer jacket starts to melt about the same time/temperature the plastic heat-resistent ABS plenum starts to soften and collapse in on itself under vacuum... just upwards of 350F.
My laser pointer infra red heat sensing gun says the TB/plenum area can run as high as 190F when idling for extended periods with the hood closed on a a hot day. But after the car is rolling and cooler air starts to circulate in the engine bay it's closer to 155F. When everything's working on water-cooled aluminum engine components they will always be cooler on their outside surfaces than the thermostats temperature setting, even at idle on a hot day. Never higher. If you have a 90C (194F) thermostat you'll be hard pressed to find an external aluminum engine component that is much above 175F and if you have an 80C thermostat (176F) the temp will hover in the 155F area. And those external temps are marginally lower when the car is under way.
And if any car's intake plenum, TB or immediate vicinity is above 275F, that little RJ11 phone cable expanding sealer ring will definately be the very least of that car's worries cuz he's either out of water or in the midst of an engine fire.
Other than a smidge of shrinking these things look as good after being in for 4-5 months as the day they were installed.
The RJ11 outer jacket starts to melt about the same time/temperature the plastic heat-resistent ABS plenum starts to soften and collapse in on itself under vacuum... just upwards of 350F.
My laser pointer infra red heat sensing gun says the TB/plenum area can run as high as 190F when idling for extended periods with the hood closed on a a hot day. But after the car is rolling and cooler air starts to circulate in the engine bay it's closer to 155F. When everything's working on water-cooled aluminum engine components they will always be cooler on their outside surfaces than the thermostats temperature setting, even at idle on a hot day. Never higher. If you have a 90C (194F) thermostat you'll be hard pressed to find an external aluminum engine component that is much above 175F and if you have an 80C thermostat (176F) the temp will hover in the 155F area. And those external temps are marginally lower when the car is under way.
And if any car's intake plenum, TB or immediate vicinity is above 275F, that little RJ11 phone cable expanding sealer ring will definately be the very least of that car's worries cuz he's either out of water or in the midst of an engine fire.
Other than a smidge of shrinking these things look as good after being in for 4-5 months as the day they were installed.
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