Why Is Your Car Shakes When Idle : Causes & Fixes

Car Shakes When Idle

Car shaking when idle can be a complex problem, as it can have many serious causes and can greatly affect the functioning of the engine.

Engines are an important part of vehicles. But in many cases, due to some problem, the engine of the vehicle starts vibrating at idle, and the jerk or vibration stops when the speed increases. When your car has such a problem, you may have wondered, “Why does my car shake at idle?” In this post, we will discuss the reasons why a car shakes when idle and how to troubleshoot this problem.

Why Is Your Car Shakes When Idle?

The most common causes of a car shaking at idle are engine misfiring or broken/loose engine mountings.

Actually, the problem of a car shaking at idle refers to vibration or shaking in the car at idle. This problem is especially common when a vehicle is parked and the engine is running, but the car is not in motion. When the car is idling, these vibrations can be felt through the steering wheel, seats, or the entire body of the car. Shaking of the car at idle is a sign of engine failure, due to which the car engine is experiencing jerks. It may also indicate a mechanical problem with the engine.

In many cases, shaking at idle causes the engine to shut down completely, requiring a restart. Due to engine shaking at idle, the engine RPM drops below its normal state, or the RPM needle bounces up and down.

Causes of Car Shakes When Idle

If your car shakes while idling, common causes are engine misfires, a faulty fuel pump, a faulty fuel injector, a faulty spark plug, other electrical problems, incorrect engine timing, a damaged engine valve, a faulty throttle body, or a bad TPS sensor.

Let us understand the reasons for this problem in detail so that you do not get confused about it.

1. Faulty Fuel Pump

fuel pump location

The fuel pump plays a vital role in the efficient operation of the vehicle’s internal combustion engine. The fuel pump sends fuel to the engine’s fuel injectors at high pressure, which enables the fuel injectors to spray fuel into the engine’s internal combustion chamber and start the engine efficiently. But a faulty fuel pump can also cause the car to shakes when it is idle.

2. Faulty or Clogged Fuel Injectors

Faulty Fuel Injectors

At times, faulty or clogged fuel injectors can also cause the car shakes when idle. Because clogged or faulty fuel injectors are unable to spray a sufficient amount of fuel when the engine is running at idle, fuel pressure during acceleration allows the fuel injectors to function properly.

3. Faulty Spark Plugs

Symptoms Of Bad Spark Plugs & Replacement Cost

Spark plugs play an important role in starting the engine. The spark plug ignites the fuel mixture in the internal combustion chamber of the engine with a spark, and the engine starts successfully. But in many cases, faulty spark plugs are not able to ignite the fuel mixture sufficiently, causing the engine to misfire at idle and engine vibration or knocking. Hence, faulty spark plugs can also cause a car to shakes when idle.

4. Other Electrical Issues

There can be many other electrical issues other than the car shaking when idle. Such as faulty distributors, ignition coils, spark plug cables, sensors, and the ECU. Because a faulty ECU in a car can badly affect the functioning of the engine, and a faulty distributor, ignition coils, and cables can badly affect the functioning of spark plugs. This problem often occurs in gasoline engines.

5. Damaged Engine Valves & Piston Rings

engine valves

As such, every part plays an important role in the efficient operation of the engine. But among the internal parts of the engine, the head valves and piston rings are the main parts. In many cases, the head valves or piston rings of the engine are slightly damaged, so these can also cause the car shakes when idle.

Because when they are slightly damaged, the engine starts losing compression and when damaged more, the engine can vibrate or jerk due to misfire during acceleration and the problem of white smoke from the exhaust pipe also starts.

6. Incorrect Engine Timing Adjustment

timing chain

Correct timing adjustment of the engine’s crankshaft and camshaft is essential for efficient engine starting. But in many cases, for whatever reason, a slight wrong timing adjustment of the engine’s crankshaft and camshaft goes wrong. A slight wrong  timing adjustment of the engine allows the engine to start, but a slight timing adjustment causes the car to shakes when idling.

7. Damaged Motor Mount

Used to install the engine and transmission in the car and to reduce the vibration of the engine in the car cabin. Motor mounts attach the entire engine and transmission to the chassis of the car.

Hard rubber is used between the motor mounts, which absorbs vibrations and shocks from the engine and holds it tight. But sometimes the motor mounts get damaged with age, and the rubber between the motor mounts gets torn and the engine starts taking vibrations and jerks. This Is Why A Damaged Motor Mount Can Cause The Car Shakes When Idle.

8. Clogged Air Filter

Clogged/Dirty Air Filter

Often, a clogged air filter can also be the cause of a car shaking when it idles.  Because air is needed to ignite the fuel in the internal combustion chamber of the engine, the engine air intake system mixes air into the fuel mixture by pulling it through the air filter. But a clogged air filter can throw off the ratio of air to fuel in the engine. And the engine may misfire at idle.

9. Faulty Oxygen Sensor

oxygen sensor

The oxygen sensor plays an important role in the operation of the internal combustion engine in vehicles. The oxygen sensor sends a signal of the amount of oxygen in the engine’s emissions to the ECU of the vehicle, so that the ECU of the vehicle sends the right amount of fuel mixture to the engine and the engine operates efficiently. But a faulty oxygen sensor can disrupt the engine’s combustion function. Hence, a faulty oxygen sensor can also cause a car to shake when idle.

10. Faulty Throttle Body & TPS Sensor

Throttle Position Sensor

The throttle body controls the acceleration of the engine, and the throttle body valve directs air into the air intake system of the engine according to the acceleration. But a bad or dirty throttle body can throw off the air-fuel ratio in the engine. A faulty TPS sensor can also affect the functioning of the throttle body. Hence, a faulty throttle body or TPS sensor can also cause the car to shake when idle.

How To Fix Car Shakes When Idle

The first thing you should do to fix a car that shakes when idle is get the cause checked by a professional mechanic.

  • Check & Replace Spark Plugs: The first thing you should do is check the spark plugs in the engine. If spark plugs are worn or dirty, they should be cleaned or replaced with new ones.
  • Check and replace the spark plug wire and ignition coil: You should also check the spark plug wire and ignition coil. If these are faulty or damaged, they should also be considered for replacement.
  • Check Fuel Pump and Fuel Filter: One of the main reasons a car shakes when idle can be a faulty fuel pump or fuel filter. Therefore, the fuel pump and fuel filter should be checked. If any of these parts are defective, they should also be replaced.
  • Clean Throttle Body and TPS Sensor: To fix this problem, you should clean the throttle body and TPS sensor as well. If the TPS sensor is bad, a replacement should be considered.
  • Clean fuel injectors: This can also be caused by faulty or clogged fuel injectors on the engine. So clean the fuel injectors. If needed, consider replacing the fuel injectors as well.

To repair internal engine damage, you will need to check the engine timing adjustment. Along with this, the head valve and piston ring will also have to be checked. If there is a problem with any one of these, it can only be rectified by engine overhauling by a professional vehicle mechanic and becomes more costly and time-consuming.


Q. How do you fix a shaky idle?

If your car shakes at idle, you can get rid of this problem by cleaning or replacing the spark plugs, fuel filter, and injectors. But if the fault persists, you should take your car to a professional auto mechanic. This problem can also be due to some other mechanical fault.

Q. What is the most common cause of rough idle?

The most common causes of rough idle are engine misfires or loose or cracked engine mountings. Often, engine misfires can be caused by bad spark plugs, fuel system failure, or any other electrical problems.

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