Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Corolla: Weird shaped rubber boot from air cleaner to throttle body

On my early 90’s Toyota Corolla there is a big rubber boot-like-thing which routes the cleaned air from the air cleaner to to the throttle body intake. You’d think it would be just a big round tube or a rectangular duct from the air cleaner to the throttle body. But no, it is very weird looking. The only thing that pokes into it is a small sensor which I think measures the intake air temperature.

It has two appendix-like things that seemingly are designed to simply poke out and consume whatever available engine space was there, and for no apparent reason that I can see. These appendages not connected to anything other than the duct itself, they are just THERE to provide empty space off both sides of the duct! One of these rubber appendages is sort of box shaped, and the other is shaped like an actual human appendix. Long and narrows to a point. I’m not making this up!

Anyway, what is the purpose for the the weird shapes? Any ideas why Toyota designers didn’t just use a simple round or rectangular duct shape to route the air from the air cleaner to the throttle body?

Those wierd appendages on the intake duct are harmonic dampeners. During research they probably found at a certain air velocity entering the duct the duct would start making noise. So those features were added to the duct to eliminate the problem.

On some exhaust systems you’ll see a mass of steel bolted somewhere on the exhaust system hanging off to the side doing nothing. Another application of a harmonic dampener.


Tester is likely right. I have a long plastic pipe on my intake hose for a 95 cirrus. The air buffeting or harmonics can cause poor readings on the airflow meter and basically make it useless. These are added to stabilize air flow for better electronic readings.

Tester is correct. I cannot remember their official name (I think it starts with “H”) but they’re baffles, intended to smooth out the pulses natural to the air stream, reducing noise from the intake manifold. The sensor may be the Mass Airflow sensor, although I don;t have access to a technical reference to look yours up.

Below is a drawing that shows what mine looks like. Sort of like a square banana. I’m inclined to want to make an iinappropriate joke, but I’ll refrain, this being a family forum.

WE humans have the same air baffles that don’t seen to make sense being there.
They’re called sinuses ( nasal cavities ) and serve no other function than described for your car.
My 08 Expedition has many along the intake snout.

You only notice their purpose when they’re not there or , as in the case of human sinuses, all plugged up.

Sinuses actually serve a valuable and necessary function. They and the hairs in them filter out the dust, dirt, pollen, etc. from entering out lungs, and sinuses alsl moisturize and temperature-stabilize air entering the lungs. Arctic Parkers act in that sense like extended sinuses when the snouts are out, creating an additional pathway for the air to warm before entering the nasal passages.

I thought they might be used to sort of store extra clean air, so it would be there ready to go when you stepped on the gas in hard acceleration. The air cleaner might not be able to pass air quickly enough on hard acceleration, and having some extra air already passed through the air cleaner ready to take up the slack, I could see that being helpful. But it’s just to reduce acoustic noise mainly? I guess that makes sense, especially if the acoustic noise would cause the airflow sensor to misread. Thanks to all for the replies. BTW, the early 90’s Corolla version is much more weird looking than the diagram posted by mountainbike of the Scion’s. Maybe they’ve figured out how to make the air flow meters less sensitive to acoustic vibration.

Chrysler calls them resonators, here is a drawing of one on a Cirrus 2.5L.
They were common in the 1990’s to suppress induction noise and Chrysler didn’t use mass air flow sensors.

There is a reason for them,I would say to quiet things down a bit-Kevin