Your car has an intake manifold that distributes air into the engine’s cylinders. Traditional designs have a fixed length and width.
But now, some vehicles have a variable intake manifold (also known as an intake manifold runner control system). The updated design varies the length of the manifold’s runners with the help of an intake manifold runner control (IMRC) valve.
How Does a Variable Intake Manifold Work?
Before you can understand the IMRC valve, you need to know how a typical variable intake manifold works. As you might guess, the technology varies the length of the intake manifold’s airflow passages, known as runners.
Varying the length of these passages allows engine performance to be fine-tuned as needed. A shorter manifold forces the airflow to undergo a tumbling effect that provides more horsepower at high engine speeds. On the other hand, a longer manifold provides more torque and better fuel economy.
There are many different variable intake manifold designs in use today. Most systems have flaps (or butterfly valves) inside the manifold that vary the runner length. An electric or vacuum-operated actuator controls the flaps.
On vehicles where a vacuum source is used, a solenoid supplies vacuum to the actuator.
Usually, the flaps control access to two separate pathways for airflow: one short and one long. Some vehicles may employ a different strategy, such as blocking off a portion of a single passage.
Regardless of the system design, a computer—often referred to as the powertrain control module (PCM)—operates the flap actuator. Most systems use a sensor or switch to provide the PCM feedback on the position of the actuator.
Also, the PCM gets data regarding vehicle operating conditions from other engine management sensors (e.g., the throttle positions sensor). The collection of sensors allow the module to make informed decisions regarding system operation.
What is an Intake Manifold Runner Valve?
But wait—what is the IMRC valve exactly? The term usually refers to the IMRC actuator, but some vehicle manufacturers may use the phrase to describe the solenoid instead.
Basically, the IMRC valve is the part of the system that opens and closes the flaps inside the intake manifold. Depending on the layout, the engine may have multiple IMRC valves or have only one valve.
It’s important to note that automakers have a bunch of different names for their IMRC valves. For instance, Ford often calls the device an intake manifold runner control (IMRC) valve, while Chrysler calls the component an intake manifold tuning valve.
Symptoms of a Bad Intake Manifold Runner Valve
A problem with the variable intake manifold system, such as a bad IMRC valve, can cause several problems. Here are the most common:
Check Engine Light
When the PCM perceives a problem with the IMRC valve or its circuit, the module will turn on the check engine light and store a diagnostic trouble code (DTC) in its memory. In many cases, an illuminated check engine light will be the only indicator that the valve is faulty.
Engine Performance Problems
A faulty IMRC valve can throw off the engine’s air/fuel mixture, leading to performance problems. Examples include a rough running engine, an unstable idle, and a lack of power.
Reduced Fuel Economy
The IMRC system is designed to boost both fuel economy and engine performance. A faulty IMRC valve can prevent proper system operation, leading to a reduction in gas mileage.
Can You Continue to Drive with a Bad Intake Manifold Runner Valve?
Technically, you can usually drive with a bad IMRC valve. But you shouldn’t continue to do so for long. As previously mentioned, the problem can trigger the check engine light—and that will cause your car to fail a state emissions test.
What’s more, in some instances, a faulty IMRC valve can damage other parts of the vehicle, such as the catalytic converter. That’s why it’s a good idea to address the problem right away.
For more information on variable intake manifolds, check out this video on the Ford IMRC system: