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Your car uses a mixture of fuel and air to run, and it's important to ensure both substances are reaching your engine properly. To achieve the right amount of air and the right quality, your vehicle uses an air box which is an intake chamber with hoses leading to the intake ports. Your car’s plenum works in conjunction with the air box to ensure the air is reaching the intake manifold efficiently so as to ensure the best performance.

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It seems like an easy process: your vehicle takes air, mixes it with fuel, and you drive to your destination. In a nutshell, your air box works by scooping air and making sure the right amount reaches the engine, while the plenum maintains the right air pressure so that it's evenly distributed to each intake port. When these two parts are working together, you get great economy and performance, but when they aren't, it's time to replace them!

Thankfully, when it comes to replacing either of these parts, they are quite easy to identify. Your air box is usually made of black plastic and is, as the name would suggest, a rectangular box. There are less common air box designs that are more of a cone shape and some are like a long rectangle, but almost all are relatively easy to identify if you look for the filters. On the other hand, your plenum can be a little more difficult because it can be made of plastic or aluminum, and can take a number of shapes. The easiest way to find it is to look for the part that your air hose goes into.

Unfortunately, you do need to know what each part looks like because they will need to be replaced one day. The need to replace them can happen quickly when either of them, or both of them, are hit by debris that makes it through the air filter and causes physical damage. However, without such bad luck occurring, you will still need to replace them as they age and begin to lose efficiency. Why? Because a damaged components means your engine is no longer getting the amount of air it requires, or the air is not being distributed in the right amounts; this loss of air can lead to problems like an acceleration lag or even stalling.

Of course, if you are unlucky enough for either the plenum or the air box to be damaged by debris, then you will easily see the physical damage. You can tell when your air box and plenum are beginning to show their age if you look for visible wear and tear, like holes, splits or simply a rough-around-the-edges look. There is an easy rule of thumb: the more holes, cracks or other damage to each part, the less efficiently your engine is receiving air and the less efficiently it is working!

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Average rating:  4.5  4.4 - 7 reviews
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4.5 of 5
2002 Toyota 4Runner / Posted by Adam (Albuquerque, NM) /

Fits perfect on my '02 4Runner Limited.

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