Uneven engine operation: discover the most common causes

It can be said that the engine is the heart of every vehicle, which is why it is extremely important for it to operate reliably and steadily. Unfortunately, drivers often encounter uneven engine operation, regardless of whether we are talking about a diesel engine or a spark-ignition engine. This phenomenon manifests itself through typical jerking, making it easy to diagnose. Uneven engine operation is usually a sign of a malfunction—either minor or major—so this issue should never be ignored. What could be the cause of such a condition?

Is uneven engine operation something that should concern drivers?

Before we discuss the most common causes of uneven engine operation, let's answer another question: is an engine that runs unevenly a cause for concern? The answer is clear: yes, it is a situation that should not be ignored, as it may be caused by a serious malfunction that could escalate into a costly drivetrain failure. It is particularly undesirable when the engine runs unevenly for an extended period during every trip—this is a signal that you should promptly visit a workshop for diagnosis and repair.

Uneven engine operation – causes depend on the type of engine

The causes of uneven engine operation can vary—mainly due to the type of engine design. Different components are responsible for this issue in gasoline-powered vehicles, others in diesel engines, and there are also additional factors in cars equipped with LPG systems. Below, we will discuss all the scenarios for why the engine runs unevenly for each type of fuel.

Causes of uneven operation in a gasoline engine

Let's start with uneven operation in a gasoline engine. Where should you look for the culprits?

• Worn spark plugs – Checking the condition of the ignition system is fundamental when dealing with uneven operation in a gasoline-powered engine. This is because spark plugs in poor condition may have too large a gap between the electrodes, resulting in irregular engine operation. Every driver should remember to replace the spark plugs from time to time—every tens of thousands of kilometers.
• Ignition coils – Staying with the ignition system, ignition coils should also be mentioned, as their malfunction manifests as jerking during acceleration and uneven operation when the car is idling.
• Ignition wires – Silent culprits of uneven operation in a gasoline engine. They can result in misfiring, which, in turn, causes the engine to run unevenly. Wires should be replaced every few years, though cleaning them may also yield the desired result.
• Worn fuel pump – When worn out, the driver will feel the engine running unevenly, especially during acceleration.
• Clogged fuel filter – Jerking and uneven engine operation in gasoline engines also occurs when there is a fuel system failure. Most often, this is caused by a clogged fuel filter, which happens quite frequently because drivers tend to forget to replace this component regularly.
• Faulty throttle body – This component regulates the amount of air entering the engine. If its operation is disrupted, it will cause the engine to choke. In such cases, the throttle body needs to be replaced or repaired.
• Air filter – Another source of uneven engine operation may be a dirty air filter, which should be cleaned or replaced with a new one.
• Exhaust system – Problems with the catalytic converter or bent exhaust pipes can also cause the engine to run differently than it should. A metallic sound during engine operation or shutdown is a sign that something is wrong with these components.

Uneven engine operation with LPG – causes

Uneven engine operation also occurs in vehicles equipped with LPG systems. What are the causes?

• Gas quality – The more sulfates present, the higher the chance that the membranes in the reducer could rupture, leading to engine operation issues.
• Ignition wires – Similar to regular gasoline engines, the wires may also be the culprit. However, in LPG systems, they are subjected to greater loads, so they should be replaced approximately every 30,000 kilometers.
• Gas supply lines – Due to continuous use, the lines may start to crack over time, resulting in system leaks and improper fuel dosing.

Uneven operation in a diesel engine – what could be the cause?

Diesel engines are a different story altogether, as their construction differs significantly from gasoline counterparts.

• Worn injectors – Is the engine running unevenly at low RPMs? This could be a sign that the injectors are malfunctioning. Worn injectors will present similar symptoms when idling. Issues can also stem from injector seals, which cause leaks and, consequently, loss of compression. Injectors may cause jerking, so it’s worth ensuring their proper condition in advance by using a good cleaning and maintenance product, such as TEC 2000 Diesel Injector Cleaner, which is based on an innovative formula that thoroughly removes impurities from poor-quality fuels and dirt accumulating in the injector nozzles. This product extends injector life and protects them from clogging.

Clogged fuel filter – Diesel engines face much tougher challenges, especially in cold temperatures (when paraffin precipitates from diesel fuel, restricting or completely blocking fuel flow, clogging the filter).

• Faulty glow plug – This can cause jerking, engine vibrations, excessive smoke, and difficulty starting the engine. It is recommended to replace glow plugs every 100,000 kilometers, although service can be considered earlier, around 70,000 kilometers.
• Injection pump – A malfunction in this component leads to uneven operation of a diesel engine. It's important to note that repairs can be expensive, so to avoid problems, high-quality fuel filters should be used.

Uneven engine operation – countless potential causes

What we’ve discussed above is not the whole story. The topic of uneven engine operation, both at idle and while driving, is very complex. Factors such as unmetered air, damaged high-voltage wires, poor vehicle grounding, a damaged cylinder head, misaligned timing, faulty EGR valve operation, or resistance in engine accessories can also contribute to the problem. Due to this complexity, if any irregularities in engine operation are detected, it’s important to visit a service center as soon as possible for diagnosis and repair.

How to prevent uneven engine operation? Regular cleaning is key

It’s important to remember to regularly maintain various systems using flushes and other cleaning and conditioning products. Adding these products will help keep components in good condition and prevent a variety of malfunctions. Consistency is key. If you plan to take care of your vehicle, check out TEC 2000's offerings. On our website, you will find a variety of products that will help protect specific systems from accumulating contaminants and more. Below is a list of available products—discover their properties and prevent uneven engine operation in your car and beyond.

• Engine Flush – An innovative engine flush that conditions the drivetrain, removing contaminants from lifters, pistons, and the oil gallery.
• Diesel Injector Cleaner – A diesel injector cleaning product mentioned in one of the previous paragraphs.
• Diesel System Cleaner – An additive for diesel engines that reduces the effects of poor fuel lubrication, while also cleaning and conditioning the engine and fuel system.
• Oil Booster – An oil additive that reduces lubricant wear. It prevents oil oxidation and hardening while also reducing friction in a cold engine.
• Fuel System Cleaner – A gasoline additive with water-binding properties. This product helps dry out the fuel system and extends the life of injectors.
• Fuel Injector Cleaner – A gasoline injector cleaner that can serve as a last resort before disassembling injectors.
• Induction Cleaner – An intake system cleaner that removes contaminants from the turbocharger, intake manifold, control valves, and throttle body.