Problems With a Dirty Intake Manifold

by Mitchell Brock
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The intake manifold is an essential part of the car engine. It is a series of tubes that attach to several engine components and delivers air to the cylinders or combustion chamber. Along with air delivery, the intake manifold also is a passageway for the fuel mixture, and distributes both the air and fuel to the cylinders. When the intake manifold becomes dirty, it shows specific symptoms during engine operation.


One of the first signs or problems that develop when an intake manifold is dirty occurs when the engine is idling. The smooth sound that you generally hear after turning on the engine is replaced by an intermittent sound. The idle begins to run roughly because of dirt or debris affecting the air and fuel mixture running through the intake manifold. The fuel filter does not remove all the foreign objects found in gasoline. These minute particles can attach themselves to the intake manifold, interrupting the flow of air and fuel into the combustion chamber of the engine.


Many times a dirty intake manifold will cause the automobile to stall when decelerating. As you come to a stop, the dirt and debris prevents the air and fuel mixture from entering the engine compartments. Once the flow of air and fuel is interrupted, the engine stalls and dies when stopping.


A dirty intake manifold can also cause one or more cylinders to miss. A miss on a cylinder occurs when it is not being properly ignited during operation. Not all dirt and debris affects the entire intake manifold. Dirt can infect only one of the tubes providing air and fuel to one cylinder head. Since that cylinder is not getting ignited, the engine compensates for the loss in power by jumping over the missing cylinder. This causes the engine to stop turning for a short time. The stoppage is so minute that it does not shut the engine off, but you can hear the problem cylinder not engaging.


A lot of times a dirty intake manifold will cause the engine to cough, which is caused by the lack of fuel mixture and air entering one or more combustion chambers. The dirt or debris has not cut off the flow of air or fuel, but limits the amount required to fully ignite the cylinder. The lack of air and fuel causes the engine to cough or backfire. The dirt limits the fuel and air, but does it inconsistently. The cylinder alternately receives a small amount of air and fuel penetrating the dirt, and then a lot of fuel and air penetrating the dirt. The inconsistent amount creates the coughing sound.


One major problem with an intake manifold is carbon building up inside the tubes of the component. The warm air oxidizes the fuel mixture over time creating carbon that develops inside the manifold tubes. The carbon can block an entire tube and cause all the symptoms previously mentioned, as well as prevent the engine from even starting. Carbon is a gummy stuff that will stick to every part of the engine. It can infect the fuel injectors, cylinders, pistons and every part of the intake manifold.

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