The intake manifold splits incoming air from the throttle body and routes it evenly to each cylinder. Its shape is tuned to improve airflow at different engine speeds.
Animated: how a Intake Manifold actually works
🔧 How It Works, Step by Step
1
Air enters the plenum
Air from the throttle body collects in the manifold's plenum chamber.
2
Runners divide the flow
Individual runners branch off the plenum, one for each cylinder, to distribute air evenly.
3
Runner length tunes the flow
Long runners boost low-end torque while short runners favor high-rpm power, and some manifolds switch between them.
4
Air reaches the intake ports
Each runner delivers its air charge to the cylinder head's intake port and valve.
🧩 The Key Parts
Plenum
Collects and evens out incoming air before distribution.
Runners
Channel air to each individual cylinder.
Gaskets
Seal the manifold to the cylinder head to prevent leaks.
Runner control flaps
Change effective runner length on variable-intake designs.
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The 50 most common check engine codes with likely cause and DIY fix cost. Sent once.
🩺 Signs of a Failing Intake Manifold
Rough idle from a vacuum leak
Loss of low-end or top-end power
Hissing or sucking noise
Coolant leak on manifolds with coolant passages
Check engine light for lean condition or runner control
⚠️ Common Problems
Gasket leak
A failed intake gasket creates a vacuum leak that leans out the mixture and roughens idle.
Cracked plastic manifold
Heat cycling cracks composite manifolds, causing leaks or coolant loss.
Stuck runner flaps
Seized variable-intake flaps hurt power and set runner control codes.
💰 Cost to Fix
$250-$900typical range to repair or replace, parts and labor
❓ FAQ
What does a vacuum leak at the intake manifold do?
Unmetered air enters through the leak, leaning the mixture and causing rough idle, hesitation, and lean codes.
Why are some intake manifolds made of plastic?
Composite manifolds are lighter, cheaper, and run cooler than aluminum, which helps intake air stay dense.
What is a variable-length intake manifold?
It uses flaps or valves to change runner length, giving strong low-end torque and good high-rpm power from the same manifold.