A rough or unstable idle

What are the possible causes?

A rough or unstable idle in your vehicle

Is your idle rough? Does the RPM have a tendency of going up and down? There are several factors that may be at the heart of the problem, and generally it is not terribly expensive to solve. Often, the most difficult part is to determine exactly what is causing the issue.

What are the possible causes?

Ignition coil
In gas engines, ignition problems (poorly synchronized sparks produced by the spark plugs) can cause a rough idle. The ignition distributor may also be responsible as it is a part of the ignition system.

Fuel injection
A seized fuel injector in a gas or diesel engine will cause the idle to feel rough since the cylinder powered by it will be defective. Also be sure to check the wiring of your injectors to make sure they are not oxidized. Oxidation of these components can also cause a rough idle.

Pressure regulator
The fuel pressure regulator (located toward the injection pump) is often the cause of idle issues.

Throttle body
Sometimes the throttle body can malfunction or become clogged, therefore preventing the butterfly valves from putting themselves correctly into place. When you accelerate, the butterfly valves open, and close when you release the accelerator. If the issue is not persistent and only occurs in cold weather, then there’s no need to be concerned. This problem is more commonly a concern for gas engines, as unlike gas engines diesel engines don’t need a throttle body (although one was added on modern blocks for technical reasons).

RIdling regulator
Yes, there exists a component who is responsible to regulate the vehicle’s idle. It is also called an idle air control actuator or idle air control valve, and is located toward the throttle body. It is possible for this part to become dirty and therefore malfunction.

Oxygen sensor
The purpose of the lambda probe is to measure the proportion of oxygen in the gas or liquid being analyzed by the engine control unit, to make sure that the engine burns its fuel efficiently and cleanly. If the lambda probe malfunctions, it can result in an abnormally slow idle.

Have you a rough or unstable idle ?


The decarbonization enables to solve it.

Preventive engine cleaning enables you to restore engine parts rather than replacing them, thereby saving vehicle owners on costly parts, such as a new turbocharger ($ 1.350 - 3.100), catalytic converter ($ 600 - 2.000), DPF ($ 600 - 2.000) or EGR valve ($ 370 - 500).

These problems result mainly from poor combustion, which stifles the engine.

So before replacing your engine parts, try Carbon Cleaning. A dirty engine as the result of carbon deposits is the new threat to vehicle performance.

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