Rough idling means that your vehicle is vibrating, producing unhealthy noises, or displaying an inconsistent RPM while it is stationary and the engine is on. The reasons for a rough idle can vary, with some being cheap, easy fixes, and some requiring more complex repair procedures.

In a healthy car, the RPM should stay between 600-1200 while the vehicle is idling. If the engine is just started then the engine RPM with be higher above 1000 rpm. For a 4 cylinder car where the engine is warmed up, the engine should idle around 750 rpm. There should also be little or no vibrations or shuddering from your engine.


Causes of Rough Idling:

1. Loose or Damaged Vacuum Hose

Many vehicles rely on a vacuum hose to assist in the processing and combustion of fuel. If the vacuum hose becomes loose or leaks, your vehicle will struggle to process burning fuel, resulting in a rough idle (often causing a higher idle speed). Sometimes you can hear a “hissing noise” with the engine running when a vacuum hose is disconnected.


2. Malfunctioning Spark Plugs

Spark Plug

Spark plugs ignite the air/fuel mixture in your engine’s combustion chamber, allowing the car to burn fuel correctly. When the spark plugs are malfunctioning, your car may vibrate or produce unhealthy noises when idling.

Common causes of malfunctioning spark plugs include components wearing over time, incorrect installation, damaged / fault ignition coils, or damaged wiring in your car’s ignition system.


3. Unclean or Damaged Fuel Injector

The purpose of your car’s fuel injector is to inject fuel into the engine cylinders. This allows for the fuel to mix with air and create the required energy to power your car.

Over time, fuel injectors can become dirty, reducing their ability to effectively transfer fuel. Sometimes a fuel injector will become partially blocked decreasing the amount of fuel entering the engine’s cylinder, or not seal correctly and leak fuel into the engine’s combustion chamber. Regular inspection and cleaning of your car’s fuel injectors will result in a much smoother idle.


4. Clogged Air Filter

air filter

A clean air filter (left) and a dirty air filter (right).

The air filter cleans the air as it enters your vehicle, removing contaminants such as dirt, sand, leaves, and dust. Over time, your car’s air filter will become clogged due to these contaminants becoming stuck. This can cause poor fuel economy, engine misfires, and rough idling.

Your air filter’s lifespan depends on your driving habits. If you drive through a lot of rough, rural terrain, the filter will become clogged at a quicker rate.



Car Servicing in Hamilton

At Grimmer Motors, we can use our huge range of diagnostic tools to quickly and accurately identify the cause of a rough idle. Our team of experienced, qualified, and skilled mechanics can then offer you quality advice and solutions. Whether it’s spark plug replacement, vacuum hose replacement, air filter repairs, or fuel injector repairs, we will strive to get your car operating smoothly again as quickly and cost-effectively as possible.

For reliable mechanics in Hamilton, contact us today!


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