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Here we look at the 9 reasons why cars jerk (with fixes) – Some are very cheap, but others, I’m afraid, will cost a lot of money.

  • Cracked Distributor Cap
  • Dirty Air Filter
  • Damaged Spark Plugs
  • Catalytic Converter Blocked
  • Gas Lines Damaged
  • Loose Throttle Cable
  • Defective Carburetor
  • Fawlty Mass Airflow Sensor

Below we’ll examine the most common reasons first and also explore the costs of each fix.

When you accelerate, your car has to burn more fuel more quickly. If your car is jerking, it means that somewhere in the mechanics of your vehicle, there is a problem that is preventing this from happening.

This can be dangerous if you are overtaking a car or pulling out from a junction. You need your vehicle to respond consistently when doing this. It’s unsafe and stressful if it doesn’t.

 1. Cracked Distributor Cap

A distributor cap is part of the car’s fuel system and where the spark plugs are located. Condensation can form underneath the distributor cap on cold days, which prevents the spark plugs from firing correctly and can result in the jerky acceleration you are experiencing.

This is most common when the car is left outside overnight, rather than when the car has been kept in a garage. It’s straightforward to check to see if this is causing the issue.

Most distributor caps are held in place by clips that you can easily open to get inside. Once inside, look for moisture and clean gently with a clean cloth and a spray of WD40.

The problem will disappear once the water has dried, but it can cause engine damage over time. If garaging your car is not an option or you are expecting cold temperatures, a thermal cover can reduce the chance of condensation.

If the distributor cap is broken or cracked, you should replace it. This is a job you can do yourself with minimal tools or expert knowledge. 

A replacement distributor cap costs around $30 -$85. If you’d rather not fit it yourself, then a mechanic will charge you about $50 in labor.

2. Dirty Air Filter

The car’s air filter acts as the first line of defense against dirt and foreign particles. Dirty filters can allow these particles to enter the engine and cause severe performance problems.

Air filters are typically checked and cleaned when you have your car serviced, but it’s worth checking if it’s been a while since that happened. It’s the cheapest replacement part on this list, but it may be you can clean the filter rather than replace it.

A replacement air filter will cost around $30 and is easy to fit. Just take out the old used one and pop in the new one in its place. Hopefully, that’ll fix the problem, and your car accelerates more smoothly from now on.

Clean filters can dramatically increase the life expectancy of your car’s engine too.

3. Damaged or Dirty Spark Plugs

Bad or dirty spark plugs can cause an engine not to ignite fuel properly, resulting in a misfire. It may feel like your vehicle shakes when you accelerate or is jerky while driving.

You might find that your spark plugs are worn and cannot ignite the fuel fast enough. Most cars have four spark plugs, – one for each cylinder – and just one dirty or broken one will cause your car engine to underperform.

It’s always best to buy a brand new set of four as it’s likely that the plugs in your engine were fitted all at the same time, and if one has failed, the others are likely to break soon as well.

Always buy a recognized spark plug brand, as they should last longer and give you better long term value for money.

A good set of spark plugs will cost $150 – $300, including fitting. You’ll need specialist tools if you want to fit them yourself.

One of the main reasons your acceleration may be jerky is because of dirty fuel injectors. Fuel injectors provide the fine spray of fuel that the spark plugs ignite.

If they are clogged up with carbon, dirt, or other deposits, they will cause the affected cylinder to misfire. If you have checked or had a mechanic check the distributor cap, air filter, and spark plugs, this could be the cause.

Most fuel injectors are good for 100,000 miles but if your car hasn’t been serviced regularly, they could fail sooner.

There are fuel injection cleaners that you can add to your gas. They work by removing carbon and other deposits. They may work depending on how badly clogged your fuel injectors are.

It is worth trying this first before getting your fuel injectors replaced, as the cost of this job is in the range of $700 – $1,500. 

The fuel injector cleaning solution only costs about $10, so it’s always worth trying that first.

If your car jerks more than just when you accelerate, this article will help diagnose the problem.

What Does It Mean When Your Car Shakes, The Fixes and Costs

5. Catalytic Converter Blocked

A blockage could be affecting your catalytic converter. The catalytic converter is part of the exhaust system that collects harmful gases and stops them from escaping into the atmosphere.

A blockage can occur when the air-fuel mixture that passes through your catalytic convert becomes too rich. 

However, this is unlikely to be the problem as a separate warning light would usually show on the dashboard, alerting you to any problem with the catalytic converter.

If you have this warning light on too and the fault turns out t be with the Cat, try to clean it first. It might need a regeneration too. A professional will charge $150 for a cleaning cycle. This can be good value as new catalytic converters are expensive

catalytic converter blocked can cause jerkiness

A new catalytic converter can cost anywhere from $500 to $1,500 plus the cost of fitting. They are expensive because the ‘cat’ uses Platinum, Palladium, and Rhodium.

These are rare elements that catch the particulates before they travel down the exhaust.

Other symptoms include a rotten egg smell coming from the exhaust and decreased fuel efficiency.

6. Gas Lines Damaged

Car fuel lines are made of metal and control the flow of gasoline throughout the engine. If they are damaged or leak, the pressure can be lost and cause the car to jerk as the pipes struggle to supply the amount of fuel the engine needs to accelerate.

However, if your car’s gas lines or damaged, you would likely be aware already. You would probably already be smelling gas in and around your vehicle. You may have even noticed a puddle of gas under your car too.

Fuel efficiency would also be affected.

If your fuel lines are damaged or leaking, then you need to get your car repaired as quickly as possible. This could be extremely dangerous.

This is quite a cheap fix but a very urgent one. Expect to pay no more than $150.

7. Damaged Throttle Cables

When you put your foot on the gas pedal, a cable runs under the hood – in older cars- and increases the amount of gas released into the engine.

If the cable is worn, then it won’t be as responsive as it should be. This will result in slow reactions or, in bad cases, no reaction at all from your car.

You would probably already be aware of other symptoms of a loose acceleration cable as the pedal would feel stiff or hard to depress or even slack. 

A very cheap fix, but it’s unlikely to be the cause of the car not accelerating.

8. Defective Carburetors

The carburetor controls how much fuel and air are combined before the engine starts. Damaged carburetors can cause your car’s acceleration to jerk and will lead to poor performance overall.

Depending on your car’s model, the carburetor of your car comes with multiple jets. These jets control fuel flow in various sections of the carburetor. 

Carbon deposits can build up over time and cause engine performance problems. A good carburetor cleaner should get rid of most of the dirt and grime that could be blocking the jets.

Expect to pay $20 for a spray can of cleaner.

On rare occasions, the carburetor may need replacing. This is very costly.

9. Mass Airflow Sensor (MAF)

Most of the causes of your car jerking have been seen to be due to restricted gas flow into the engine or failure for the gas to ignite.

The Mass Airflow Sensor is different. It regulates how much air is entering the engine.

It sends and receives signals to and from the car’s computer. The computer instructs the fuel injectors on how to deliver the correct amount of fuel at the appropriate time for the proper mixture.

A faulty MAF sensor can send incorrect readings to your car’s computer, and this can either allow more or less air into your engine. The result of this is choppy speed changes and sluggish acceleration.

There are specific cleaners you can buy to get your MAF working correctly again. Don’t expect to pay more than $15 for a can.

If cleaning doesn’t free up the MAF, you may have to get it replaced. Expect to pay $150, including fitting.

In conclusion

As you can see, although there are quite a few reasons why your car is jerking when you accelerate, not all will cost a lot of money to fix. Some of the checks you can do yourself, and this could save you a lot of money in car shop charges.

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