Car Shakes When Starting Then Runs Fine: 6 Reasons and Fixes

A little jerking during the engine startup is normal. Sometimes, the car can shake vigorously during the startup. As soon as the engine is up and running, the shakiness disappears.

So, why does a car shake when starting and then run fine?

I will be covering the detailed reasons along with the possible solutions for this problem. Make sure you read till the end to get all the necessary troubleshooting ideas and tips.

Car Shakes When Starting Then Runs Fine: What Are the Reasons?

Check this long list of reasons that can cause your car to shake excessively during the startup.

1. Loose Engine Mounting

The engine in your car is bolted to the frame via multiple mounts. Over time, engine vibration can loosen the mounting bolts. If the mounting bolts are notably loose or any of the mounting brackets are displaced, the engine will sway.

When the engine is off, there will be no vibration. During the startup, the vibration in the engine will be multiplied at the mounts and cause the car to shake. Once the engine settles in speed, the sway is aligned on one side or another. So, the shaking stops after that, and the car runs fine.

Symptoms

• Besides the engine noise, there will be metal clanking noise or grinding noise from the engine bay.

Solution

1. Check the engine mounting closely. If any of the mounting brackets are off, make them straight. Use a torque wrench to tighten the mounting bolts. 

2. Fouled Spark Plugs

As spark plugs reach the top of the combustion chamber, the residue from the combustion fouls the spark plugs. Over time, this fouling decreases the effectiveness of the spark plugs. The spark plugs sometimes fail to produce an effective spark.

So, the engine doesn’t start in one go. The misfiring caused by fouled spark plugs causes the car to shake when starting. Once the fouled plug manages to spark and start the engine, the sparks tend to come regularly. So, the engine runs fine after that.

Symptoms

• The engine will misfire during the start. If you check with an OBDII scanner, it will show codes between P0300 and P0308. These are codes for misfiring issues and faulty spark plugs.

Solution

1. You have to get the number of the specific spark plug from the error code. For example, P0301 stands for an issue with the spark plug in the first cylinder. 
2. Turn the car off and open the hood. Remove the spark plug cable. Then, take the spark plug out and check it visually.
3. If the spark plug has light fouling, clean it with a spark plug cleaner. For heavily fouled or worn spark plugs, you have to replace the plug.

3. Weak Ignition Coil Pack

The coil pack is a crucial part of the ignition system. It provides the necessary voltage to the spark plugs to generate the spark. During a cold start, the coil pack may fail to provide the necessary voltage a few times.

This will cause the engine to misfire and shake the car. After the startup, coil packs may get back to their normal routine. That will eliminate the vibration of the car.

Symptoms

• The main symptom is a misfiring engine. You can be sure of it by checking the diagnostic trouble code. If the code P0351 appears, the problem is with the primary or secondary circuit of the coil pack.

Solution

1. You have to identify the number of the weak coil pack. Remove it from the assembly and swap it with another coil pack just to be sure.
2. If the swapped coil pack performs right, then the previous one was faulty. Get it tested by an experienced mechanic or replaced for a better performance.

This tutorial video may be helpful:

4. Dirty Fuel Injectors

In modern engines, fuel injectors precisely spray the fuel into the engine for efficient combustion. Over time, the injectors can get dirty, especially because of fuel contamination. As a result, the injectors fail to provide the right amount of fuel for the startup.

So, the engine hiccups during the startup. Once the engine starts, the ECU adjusts the fuel pressure to provide the right amount of fuel. The car then starts running fine.

Symptoms

• The code P0253 can appear if the fuel injector has any issues. Besides, misfiring codes will appear.

Solution

1. You have to take the car to a repair shop and get the fuel injectors cleaned. I recommend not performing this on your own unless you have extensive experience.

5. Worn Flywheel or Start Motor Pinion

The starter motor is a small yet powerful motor used to turn the engine over. When you turn the ignition key or push the ignition button, the starter motor engages with the flywheel and turns the engine. If the gears on the flywheel or the starter motor are worn, the motor will fail to establish a clean contact.

As a result, the engine will take time to start. Failed attempts to turn the engine over will shake the car. Once the engine starts, the starter motor retracts the pinion. From that position onwards, the engine will run without any issues.

Symptoms

• There will be a whirring sound while starting the engine. 

Solution

1. Take the vehicle to a repair shop. Get the flywheel and the starter motor inspected visually. If any of the gears are broken or worn, you have to get them replaced.

6. Dirty Fuel Filters

Fuel filters keep the contamination out of the engine. Doing this causes an accumulation of contaminants on the filter body. Over time, filters may lose their efficiency. As a result, the fuel passing through the filter gets reduced.

It makes the air-fuel mixture in the engine leaner. A dirty filter may cause the engine to shake while starting. After the startup, the issue often vanishes if the filter isn’t fully clogged.

Symptoms

• Along with misfiring error codes, you might get codes P0171 and P0174. These indicate the air-fuel mixture is too lean for the engine.

Solution

1. Remove the fuel filter from its housing carefully. Clean the filter thoroughly to get rid of all the grime and debris. Then, reinstall the filter. If the filter is too old and clogged, you have to replace it.

Tips to Prevent Car Shaking While Starting

Follow these tips to avoid this annoying situation.

• Perform routine maintenance to keep ignition components working properly.
• Don’t park the car in an extremely cold temperature for a long time.
• Clean oil and fuel filters periodically.
• Check for loose components before starting the car, and fix them. 

FAQs

Find answers to some commonly asked questions about cars shaking while starting.