Your car idles when it is turned on and not in motion. The vehicle can be in gear when idling, such as when you’re stopped in traffic or at a red light. Or the car may be in neutral when idling – you may have the clutch pressed in if you have a manual transmission vehicle.
Unless your car automatically turns itself off when stopped with built-in stop/start technology, you will feel your vehicle vibrating slightly when it idles. This is normal. The older the car, the more you may notice the idling vibration.
But the car shouldn’t be shaking when it idles. There also shouldn’t be a knocking noise when your car is idling. Let’s look at what causes a car to shake when idling.
10 of the most common reasons why your car shakes while idling
If your vehicle shakes or shudders while idling, look for any warning lights or indicators on the dash. Pay attention to any strange odours and look for smoke coming from the exhaust.
1. Dirty Fuel Injectors
Fuel injectors that are clogged or obstructed by dirt or carbon cannot dispense the right amount of fuel needed for combustion. This may result in rough idling.
2. Worn Spark Plugs, Spark Plug Wiring, Ignition Coil
The spark plugs provide the ignition needed to start the engine, so if one is faulty or worn, the engine may react and cause the shaking.
Similarly, an ignition coil that is worn down over time may cause misfires.
3. Clogged Air Filters
Over time, your car’s air filters become full of dust and dirt. This then prevents proper air flow needed for the fuel mixture for combustion and could also lead to rough idling.
4. Air in the Fuel Lines
If you have a loose or missing gas cap, air will get into the fuel lines and may cause the engine to shake while idling. Also, excess air may enter the fuel mixture if you have worn-out rubber hoses under the bonnet.
Too much air in the fuel mixture can cause the engine to misfire, idle roughly or turn over high RPMs.
5. Worn throttle body
The throttle body is a small housing that connects to your fuel line and engine. It controls the amount of air that enters the engine to regulate combustion. The engine’s idle speed will be affected if the throttle body or its sensors are faulty or damaged. This may result in unnecessary vibration or rough shaking.
6. Oxygen Sensor
Your vehicle’s computer calculates the ideal ratio of air and fuel for the most efficient combustion process. An oxygen sensor relays information about how much oxygen is in the exhaust. If there is a breakdown in this sensor, the vehicle’s computer will receive incorrect information and affect the engine’s performance.
7. Loose or Broken Engine Mounts
The engine is held in place by an engine mount frame that is designed to absorb the vibrations of your engine running normally. If part of the engine mount frame is broken or missing, you’ll feel the engine’s vibrations more.
8. Loose Battery Cables
There may be unnecessary cranking when you start the engine due to an insufficient charge from the battery. This might be caused by a battery cable that has come loose from the terminal.
9. Damaged or Slipped Belt
The fan belt – also called the serpentine belt – is a long rubber belt that transfers power to the engine accessories – the alternator, pumps, steering lines, air conditioning compressor, fans, etc.
It is powered by the engine so if it is loose, damaged or misaligned, it can create a vibration felt through the steering wheel.
10. Catalytic converter problems
Your catalytic converter filters out dangerous chemicals and toxins that come out of your exhaust. If it’s not filtering the exhaust properly, it can cause residue buildup that causes the vehicle to rattle when idling.
Can hybrid or electric cars shake when idling?
As you can see from the list of reasons above highlighting why a vehicle might be shaking or shuddering when idling, many different parts could be causing the rough idling.
Many of these components are present in hybrid or electric vehicles, so you may also experience shaking when idling with a hybrid or EV.
What to do if your car shakes when idling and when to see a mechanic
There are a few things that you can do yourself to try to stop the car from shaking when idling.
First and foremost, look to see what indicator or warning lights are on the dash. This will be your first clue of whether or not you need to see a mechanic.
Next, check your fuel cap and battery cables to see if they need to be tightened.
If you’re confident checking under the bonnet, have a look to see if your spark plugs look worn, if the air filters look like they need replacing, if the engine mount shows any obvious damage, and if the fan belt looks like it’s properly in place.
It’s best to have a mechanic look over these parts for you. If you’re unsure of what’s causing the shaking, you may do more damage by tinkering with the engine and parts yourself.
If there is no foul smell and no smoke coming from the exhaust, you can probably safely drive your vehicle to the mechanic. If you’re unsure, just give us a call on 0800 227 762 or email [email protected].