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Rough idling: What is it and what are the consequences?

A car having a rough idle is a common problem for some vehicles with carburettor or glow plug issues.

Want to know if this is the case for your vehicle? In this article, we’ll be explaining what rough idling is, the components that cause it, and the consequences. Keep reading!


What is idling?

Idling is the minimum rotational speed of a vehicle’s engine.

Whether when starting a vehicle or when stopped at traffic lights with your gearbox in neutral, your vehicle should keep its engine revs stably idling so as not to overwork the engine, ensuring it is ready to spring into action when the gear is changed using your gearbox.

When you press down on the accelerator, your car engine will increase its revolutions per minute (RPM), and your car will no longer be idle.

Most often, when you start a car engine, it starts with a high rev count and then goes down to normal idling when the engine reaches an ideal operating temperature.


What is rough idling?

Rough idling, also known as unstable idling, happens when a component within your car engine interferes with the combustion mechanisms inside your car’s engine block, which leads to your car being unable to keep your engine revs stable and operating normally.

This problem is common for vehicles with faulty injection systems, carburettors, spark plugs or fuel supply systems.


What are the symptoms of rough idling?

  • Your car vibrating excessively;
  • Vehicle revs increasing and decreasing unstably and randomly (which you’ll be able to see on your dashboard rev counter);
  • Your car seems to lose power when pulling off.


What causes rough engine idling?

1. Spark plugs

The first components you should check if your car begins rough idling are its spark plugs, especially if your vehicle loses power when pulling off.

Spark plugs should be replaced every 30 000 km or 60 000 km, depending on your car manufacturer’s specifications.


2. Fuel filters

If your engine remains unstable once you’ve started your car, you may have a problem with your air or fuel filter.

These may be clogged with debris or simply need to be replaced.


3. Improperly adjusted carburettor or valves

An improperly adjusted valve or carburettor can mean the wrong amount of fuel is being pumped into the engine, leading to rough idling.

To ensure your carburettor meets manufacturer recommendations, mechanics must use a pressure gauge kit to adjust your car’s carburettor.


4. Idle air control valve failure

Idle air control valves should be cleaned every 40 000 km, as they tend to accumulate debris.

An idle air control valve left in poor condition can lead to rough idling.



What is an idle air control valve or actuator?

An idle air control valve is a component used within fuel-injected vehicles responsible for sucking air into the intake manifold.

This component provides the exact amount of air needed to produce combustion within the engine when combined with the fuel.


What are the main problems found in an idle air control valve?

  • The solenoid short-circuiting;
  • Metal components corroding;
  • Mechanical damage caused by debris.


What are the consequences of rough idling in car?

Rough idling can lead to damage:


What should you do if your car is rough idling?

If you find that your vehicle shakes excessively, has unstable engine speeds, or loses power when pulling off, you should take it to a trusted or manufacturer-approved mechanic to see if they can solve the problem.

Bear in mind that by seeing a mechanic, you are preventing the problem from getting worse and spreading to other components.

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