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Signs of a Bad Intake Manifold Runner Control System

Mia Bevacqua
November 19, 2018

Cars feature all kinds of gadgetry designed to improve fuel economy and boost performance. The intake manifold runner control system — which often goes by other names, such as a variable length intake manifold — is one such innovation.

Signs of an intake manifold runner control failure

A failure in the intake manifold runner control system can cause several problems. These are some of the most common.  

  • Illuminated check engine light: If the car’s computer detects a problem with the system, it will turn on the check engine light.
  • Poor engine performance: An engine needs the right amount of air and fuel to run properly. If the butterfly valves within the system are stuck, the engine will either get too much or not enough air. This can cause all types of engine performance problems, including rough running, lack of power and erratic idle.
  • Reduced fuel economy: A problem with the system can cause poor gas mileage, as the car will adjust how much fuel it burns to compensate for improper airflow.
Get it diagnosed by a professional
 

How the intake manifold runner control system works

To understand how the system works, it’s important first to know how air enters an engine. After getting pulled through the air filter, it travels through the intake tube and throttle body to the intake manifold. 

The manifold features individual runners, which distribute air to ports in the cylinder head. From there, valves inside the cylinder head open to let air into the combustion chamber, where it mixes with fuel and is burned.

The intake manifold runner control system improves the engine airflow process, which helps performance and efficiency. Although each carmaker’s design is different, the basic concept involves opening and closing butterfly valves within the intake manifold. 

The valves divert airflow, changing the length of the runners. A longer, narrower runner allows for more power in the low RPM range. Conversely, a shorter, wider runner provides more high-end power. 

For everything to work properly, the valves must operate at exactly the right time. In most cases, when that happens is determined by the engine’s computer. Its decisions are based on data collected from various sensors. 

» LEARN MORE: Get an estimate for having your car diagnosed

How to fix the problem

A problem within the intake manifold runner control system can be caused by anything from a failed actuator to a faulty sensor. Because the technology is so complex, diagnosis and repair is best left to a professional.

There are also several other problems that can hurt your car’s fuel economy or engine performance, all the more reason why diagnosis is key.

Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.

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