Why is my car shaking when idle?

By Julia Freeman

Whenever you’re waiting to make a turn or you’ve stopped at a red light, your car is idling. Experienced car drivers will know what vibrations feel normal for their vehicle. However, there may be times when the vibrations become loud, rattling, or make your car shake. Whether you need car servicing because of a sudden noise or increasing levels of shaking, here are the principal reasons as to why your car might be shaking when idle.

Spark plugs

Worn out spark plugs are the most common reason why a car engine will vibrate or shake strangely. Spark plugs take electrical current from the ignition and create a spark in the combustion chamber to ignite the compressed fuel and air mix. If a spark plug is damaged, it can’t properly ignite the mixture and may cause the engine to misfire - which, in turn, makes the car shake.

Timing belt

The timing belt maintains the synchronisation of the crankshaft and camshaft, so they work together to open and close the engine’s valves at the correct times. If this belt fails, your car will stutter and may even stall. Ignoring this will cause serious problems down the line, as the belt snapping will cause catastrophic engine damage.


If your coolant system leaks or the coolant level has reduced, this may compromise the efficiency of the system and result in overheating. Similarly, if your water pump is failing, coolant will not be circulating to the correct degree and, again, the engine will overheat. Since metal expands with heat, any shortcomings in the cooling system will translate into rough running as friction increases, with the potential for significant engine damage or seizing.

Timing, ignition, and fuel system

If the fuel / air mixture is incorrect, this will result in poor combustion and misfiring. Issues here may range from a blocked fuel line or fuel filter through to issues with the engine management system (EMS) or ignition timing. For vehicles with a carburettor, there may be some adjustments required in the carb itself. Any of these factors can cause the engine to vibrate.

Engine mounts

The engine mounts are responsible for supporting the engine and absorbing vibrations. If they are not working properly or have suffered damage, then even normal engine vibrations will affect your car while idling. The rubber elements of the mounts can degrade over time. Notable shaking and loud noises that come from under the bonnet when you attempt to accelerate might mean it’s time to check the mounts.

The local garage you can trust

If any of these issues are worrying you, or you just want advice, then checking in for car servicing at Protyre might just be the answer you’re looking for. Our tyre professionals have years of experience and our over one hundred and fifty garages are in local, convenient locations. Talk to one of our qualified fitters at any of our garages or contact us through our website today to find out more.
We also offer free tyre checks and stock tyres from leading brands including Pirelli, Bridgestone, Sumitomo and many more at highly competitive prices.

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About the author

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By Julia Freeman
Julia is Head of Retail Marketing for Protyre and loves engaging with customers and the business as a whole to make sure Protyre is more than just a local garage.
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