Car Shakes When Starting, Then Runs Fine: 10 Reasons

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When cars shake, it often begins subtly and then worsens. If you have ever encountered this troubling occurrence, you are not alone. Many car owners have experienced a similar circumstance: their vehicle shakes during the initial engine startup but regains its stability once the engine reaches a constant rhythm. While this transient vibration can be disconcerting, it frequently leaves drivers perplexed, pondering if it’s a sign of a more severe problem or a harmless hiccup.

But what makes a car shake when starting and then run fine? In most cases, the shaking results from a failing starter or the battery has been removed. In other cases, it can be caused by dirty fuel injectors, worn-out spark plugs, damaged motor mounts, or a tire low on air pressure.

1. Faulty Starter

A starter is a device used to turn (crank) an internal combustion engine to start the engine’s operation independently. There are electric, pneumatic, and hydraulic starters.

To start a combustion engine, it must be cranked at a certain speed so that fuel and air are sucked into the cylinders and compressed.

A powerful electric ignition motor performs the process of turning. Its shaft has a tiny pinion (gear wheel) connecting with the big gear ring encircling the engine’s flywheel.

The starter is positioned low to the ground towards the rear of the engine in a front-engine arrangement.

The starter requires an intense electrical current, which it receives from the battery via thick cables. No standard manual switch can turn it on; a large switch is needed to manage the high current.

The switch must be rapidly flipped on and off to prevent hazardous and damaging sparking. Consequently, a solenoid is utilized, an arrangement in which a tiny valve activates an electromagnet to close the circuit.

How to Test Car Starter?

  • Ensure Safety: Make sure the vehicle is in the park or neutral and the parking brake is engaged. Also, keep your body parts clear of moving components.
  • Check Battery: Confirm that the battery has enough charge. A weak or dead battery can affect the starter’s performance. If the battery is low, charge it or jump-start the vehicle before proceeding.
  • Locate the Starter: The starter motor is typically located near the engine, usually at the bottom, and connected to the transmission or flywheel. Refer to the vehicle’s service manual if unsure about the exact location.
  • Inspect Connections: Inspect the starter connections for any loose or corroded wires. Tighten or clean them, if necessary, as poor connections can affect the starter’s functionality.

2. Engine Misfire

An engine misfire is when one or more cylinders in an internal combustion engine fail to ignite the fuel properly, disrupting the engine’s power delivery and smooth operation. Misfires can be temporary, intermittent, or persistent and can occur for various reasons. Here are a few common causes of engine misfires:

  • Ignition System Issues: Problems with the ignition system can lead to misfires. This includes faulty spark plugs, ignition coils, wires, or a malfunctioning distributor or distributor cap.
  • Fuel Delivery Problems: Insufficient fuel supply or improper fuel mixture can result in misfires. Some potential culprits are clogged or dirty fuel injectors, a failing fuel pump, or a malfunctioning fuel pressure regulator.
  • Air Intake Issues: An engine requires a proper balance of air and fuel for combustion. If there are any restrictions or leaks in the air intake system, such as a dirty air filter, a malfunctioning mass airflow sensor (MAF), or a vacuum leak, it can cause misfires.
  • Engine Mechanical Problems: Certain mechanical issues can lead to misfires. This includes worn piston rings, damaged valves, a blown head gasket, or a worn camshaft. These problems can disrupt the combustion process and result in misfires.
  • Computer and Sensor Problems: Modern vehicles rely on a network of sensors and an engine control unit (ECU) to monitor and adjust various engine parameters. A malfunctioning sensor or a problem with the ECU can cause misfires by providing incorrect information or failing to change the fuel and ignition timing properly.

When dealing with an engine misfire, accurately diagnosing the underlying cause is essential. This can be done using diagnostic tools, such as an OBD-II scanner, which can retrieve error codes and provide valuable information about the specific cylinder(s) experiencing the misfire. A thorough inspection of the ignition system, fuel system, and other relevant components may also be necessary.

3. Faulty Car Battery

car shakes when starting then runs fine after

Besides making your car shake when starting, a faulty car battery can cause many other problems.

They include:

Difficulty Starting the Car: If you experience difficulty starting your car, especially in the morning or after the vehicle has been sitting idle for a while, it could indicate a weak or dying battery. The battery may not have enough power to crank the engine.

Dimming Headlights and Electrical Issues: A failing battery may produce dim headlights or interior lights. You might notice a decrease in the brightness of your dashboard lights or experience problems with your car’s electrical components, such as the power windows, radio, or power locks.

Clicking Sound When Turning the Key: If you hear a clicking sound when you turn the key in the ignition, it often suggests a weak battery. The clicking noise is usually the starter motor trying to engage but not receiving enough power.

How to Test Car Battery?

To test a car battery, you can follow these steps:

  • Prepare for Safety: Ensure the engine and all electrical components are turned off, including headlights, interior lights, and the radio. Put on safety glasses and protective gloves.
  • Inspect the Battery: Inspect the battery for any signs of damage, leakage, or corrosion. If you notice any abnormalities, it’s recommended to consult a professional rather than proceeding with testing.
  • Check Battery Voltage with a Multimeter: Use a multimeter, set it to DC voltage, and connect the positive (red) probe to the positive terminal of the battery and the negative (black) probe to the negative terminal. Take note of the voltage reading.
    • A fully charged battery should read around 12.6 to 12.8 volts.
    • If the voltage reads below 12.4 volts, it may indicate a partially discharged battery.
    • A reading below 12 volts generally indicates a low or dead battery.

Load Testing (Optional): While a voltage reading can provide some information about the battery’s condition, a load test is more comprehensive. You can use a battery load tester for this purpose. Follow the instructions provided by the load tester to connect it to the battery and then activate the test. The load tester will apply a simulated load to the battery and measure its performance.

    • If the battery voltage drops significantly during the load test, it suggests a weak or faulty battery that may need replacement.
    • Some load testers also provide a rating or grading to indicate the battery’s health.

Interpret the Results: Based on the voltage reading and load test results, you can determine if the battery is in good condition, partially discharged, or needs replacement. If the battery consistently shows low voltage or fails the load test, it’s likely time for a new battery.

4. Loose Engine Parts

When you start a car, the engine undergoes various processes, such as ignition, fuel combustion, and initial warm-up. If there are loose engine parts, such as spark plugs, engine mounts, or belts, they can cause vibrations and shake during the starting process.

For example, if a spark plug is loose or damaged, it may not fire properly, leading to engine misfires and rough idling. This can cause the car to shake when starting. Similarly, if engine mounts are worn out or loose, they may fail to dampen the engine’s vibrations effectively, resulting in noticeable shaking during startup.

Additionally, loose belts, such as the serpentine belt that drives various engine accessories, can cause vibrations and shake. If the belt slips or is misaligned due to being loose, it can create irregular movements in engine components, leading to shaking during startup.

5. Loose Car Components

Several components in a car’s engine and drivetrain can contribute to vibrations or shaking if they are loose or improperly secured. Here are a few examples of loose car parts that could cause shaking during startup:

  • Spark Plugs: If the spark plugs are loose or improperly seated, it can lead to engine misfires, resulting in shaking or rough idling when the car is started.
  • Ignition Coils: Loose or faulty ignition coils can cause irregular firing of the spark plugs, leading to engine misfires and shaking during startup.
  • Engine Mounts: Engine mounts are designed to secure the engine and dampen vibrations. If an engine mount becomes worn or loose, it can cause excessive engine movement during startup, resulting in noticeable shaking.
  • Exhaust Components: Loose or damaged exhaust system components, such as a broken or disconnected exhaust pipe or a loose muffler, can lead to vibrations and shaking as the engine exhaust flows unevenly.
  • Belts and Pulleys: Loose or worn belts and pulleys, such as the serpentine or timing belt, can cause the engine to vibrate or shake during startup. This is due to the improper rotation of engine accessories or a misaligned timing belt affecting engine timing.
  • Loose Suspension Components: Loose or worn suspension parts, including struts, shocks, control arms, or stabilizer links, can cause vibrations and shaking that may be felt during startup.

6. Alignment and Balancing Problems

A tire problem can potentially cause a car to shake when starting. Several tire-related issues can lead to this shaking sensation:

  • Imbalanced Tires: If the tires are not balanced correctly, it can result in uneven weight distribution, leading to vibrations and shaking when the car starts moving. Imbalanced tires can occur due to uneven tread wear, improper installation, or hitting a curb or pothole.
  • Wheel Misalignment: When the wheels are not correctly aligned, it can cause the vehicle to vibrate or shake. Misalignment can result from hitting an object, driving on rough terrain, or general wear and tear. Improper alignment can put uneven stress on the tires, resulting in shaking during acceleration.
  • Tire Wear or Damage: Worn-out or damaged tires can also contribute to shaking during startup. If the tires have uneven tread wear, bulges, or flat spots, it can cause imbalances and vibrations. A tire with a belt separation or a bubble can also cause shaking.

7. Issues with Suspension

car shakes when starting then runs fine after

The suspension system provides stability, smoothness, and control while driving. Suppose there are issues with the suspension components, such as worn-out or damaged shocks, struts, bushings, or control arms. In that case, it can lead to vibrations and shaking, especially when starting or accelerating.

When you start the car, the engine produces a torque that transfers to the wheels, causing the vehicle to move. If the suspension system is compromised, it may struggle to absorb the initial force, resulting in shaking or vibrating sensations. Additionally, suspension issues can affect wheel alignment, further contributing to vibrations.

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