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Some car shakes are common, especially when you first start the engine. A cold start is when the engine temperature (engine oil and engine coolant temperature) has cooled down to the surrounding temperature. 

A cold start puts a load on all parts of an engine, such as; the fuel pump, oil pump, coolant pump, and fuel ignition system, which can cause shaking.

This load is exerted because the fluids’ low temperature is harder to circulate and pump through the system. Besides that, the engine starts on electrical energy provided by the battery, which is less than the electrical power produced by the alternator. This strain causes the engine to shake a little, which is normal. 

However, excessive shaking when the car is cold is a sign of problems. Bad engine mounts are the most common cause. Other lesser common issues include bad fuel, worn belts, bad injectors, bad ignition systems, and faulty sensors. There are some other uncommon causes. 

Let’s get into the details.

5 Reasons Your Car Shakes On A Cold Start

Engine Mounts

Engine mounts hold the engine to the car’s chassis. It is made up of steel and rubber. The steel is used to provide strength, and the rubber absorbs all the vibrations and resonance of the engine, which come from the pistons. 

The rubbers on the engine mounts have a lifespan because rubber is exposed to heat from the engine, water, dust, and dryness. Over time, the rubber is bound to get worn, dry up, soften, crack, or even break apart. 

Sometimes the engine mount itself gives away after prolonged use and abuse. If any engine mount is worn, damaged, or broken, this causes the car frame to receive more vibrations from the engine’s vibrations.

Figuring It Out

Put the car in reverse, hold down the brake pedal press the gas pedal slightly (while releasing the clutch for manual transmissions). If there is a loose or damaged engine mount, then car rumbling or shuddering will be felt primarily from the side where the engine is mounted. 

Get the engine RPM well above the idle RPM to confirm the engine vibrations increase with the RPM. These vibrations are most noticeable in cold starts or with a cold engine because the engine is not at optimum temperature and is under load to get the temperature and idle up to optimum readings.

Repairing

The engine mounts are steel brackets mounted very carefully and strategically using a set of tools and equipment. If the cause of car vibration in the reverse gear is an engine mount, then you should have it checked by a mechanic and have a professional work on it because it will have to be changed. 

The engine mounts will cost between $50-$150, and the labor costs $200-$400, depending on the car’s make and model.

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Engine Faults

The engine mounts may be fine, and the different aspects of the engine could contribute to the car vibrations. These include; faulty throttle body, poor fuel pressure, and bad ignition. Let’s review each to find out the function and symptoms and how to tackle them.

Throttle Body

Four things within the throttle body ensure a proper air-fuel mixture in the correct ratios.

– MAP Sensor

The Manifold Absolute Pressure monitors the vacuum in the intake manifold and air intake hoses, the load that must come in through the air control valve, and the air intake hoses. If this is faulty, the ECU lets the wrong amounts of air through the air control valve, which may cause the car to feel shaky during cold starts or idling with a cold engine.

– TPS

The throttle Position Sensor controls the air control valve depending on the RPM requirements and the amount of gas pedal pressed. The sensor going bad can result in a car shake when the car idles with a cold engine.

– MAF

The Mass Air-Flow sensor measures the amount of air flowing past it and helps the ECU determine how much fuel is to be mixed. The sensor’s fault results in incorrect ratios causing RPM drops and engine vibrations.

– IACV

The idle Air Control Valve works as the name implies. The air control valve works to let in the air required by the RPM and loads.

– Coolant Temperature Sensor

This senses the coolant temperature and makes the engine work more to increase the coolant temperature until it reaches the required temperature. A failing coolant temperature sensor causes cold coolant to circulate in the engine. A cold engine makes the car feel shaky.

Figuring It Out

This can be easily diagnosed by connecting a diagnostic tool to the OBD port of the ECU, and it will show the specific errors for each.

Repairing

Each sensor costs around $20-$150 and can be easily changed.

Clean the throttle body while you’re at it because a dirty throttle body may cause a reduction in airflow and a drop in RPMs or the engine struggle to maintain them.

Faulty Ignition System

The ignition coil, ignition coil plug wires, and spark plugs make up the ignition system. The ECU controls the ignition timing, and these parts carry it out. Any damage, wear, and faults within the system won’t ignite the fuel properly during combustion, causing a power loss.

This creates terrible ignition timings and results in misfires, and the RPM and power drop under loads. Spark plugs get a build-up of carbon and wear down over time. The wires’ insulation may become worn against metal, causing an arc jump and loss of spark intensity in the combustion chamber.

The ignition coil may not get enough electricity due to damage or various reasons.

Figuring It Out

Engine knock or premature combustion is a sign of bad ignition timing. Do you feel irregular acceleration or sudden jumps in power when accelerating with a cold engine or right after a cold start? In that case, this is a sign of bad ignition timing, and it’s better if you bring it to a proper mechanic. It can be figured out for sure upon physical and technical inspection only.

Repairing

Ignition coil pack costs between $75-$400. Ignition coil plug wires cost around $20-$100. Spark plugs may set you back $50-$100 each. Labour can easily be between $20-$100.

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Old and Diluted Coolant

Cold temperatures are pretty challenging for a car. There is a good chance the coolant will freeze if old and too diluted with water, and frozen coolant cannot be circulated through the engine and causes excessive strain on the water pump. The frozen coolant will stress the engine and combustion chamber, making the car feel shaky.

Figuring It Out

You can physically inspect the coolant reservoir to check if there are any ice flakes or icing in the coolant.

Repairing

You will have to flush out your current coolant and replace it with antifreeze. Or you can mix antifreeze solutions with your current coolant. Antifreeze coolant costs about $40, and antifreeze solutions cost around $20.

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Worn Out Belts And Pumps

A serpentine belt runs through the whole engine bay so that the crank can run all the pumps, which pump oil and coolant throughout the engine.

The oil pump pumps oil through the engine, and the coolant pump pumps the coolant, brake fluid pump, and fuel pump—power steering pump, pump, what the name implies. 

If there is a worn-out serpentine belt, the pumps are not as efficient in pumping the fluids throughout the engine, and a worn-out belt puts strain on the crank, which causes car shakes.

On the other hand, the pumps sometimes get jammed or damaged due to various reasons and cause the serpentine belt to run with jitters. This stops the smooth running of the crank.

Figuring It Out

Car shakes caused by worn-out belts usually disappear as the car warms up. The vehicle shakes until the engine runs up and the optimum temperature is reached. At optimum temperature, the belt and the pumps have less strain because it is easier to pump the fluids.

Repairing

Repairing serpentine belts cost around $10-$30, and new pumps cost between $80-$200.

Conclusion

Mostly, it is a bad engine mount or transmission mount that causes car shakes during cold starts, but other lesser common reasons that cause car shakes when cold starting an engine are bad fuel, worn-out belts, or maybe just a choked air filter. 

It is recommended to take your car to an auto repair shop regularly and have it maintained and checked by a professional so that these can be avoided. Always be aware of noises and movements during cold starts and idling after cold starts. 

After the engine warms up, the engine can bear the load easily because the optimum temperature is reached, and the engine idles easily. 

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