Why isn't it jerking badly?

Motor runs rough / jerky - common causes and costs explained simply and briefly!

The most important things at a glance
  • The following Advisor refers to cases in which the engine runs unevenly / unevenly or jerks or stutters. However, if it is more of a I recommend this guide to vibrate “all over the vehicle” or “in the steering wheel”.
  • First, observe when exactly the engine is not running smoothly. It can be the case, for example, that it runs rough mainly after a cold start, while idling or during the entire time.
  • So a To run the engine properly, it needs fuel, electricity, and air. However, if the engine does not run smoothly, there is almost always a problem with one of these three points.
  • More other typical causes, required repairs and all costs incurred you will find out in the following and the linked guides!

Possible causes when the engine is not running smoothly

Especially when the outside temperature is low and the engine is cold, the engine may still seem a bit uneven for the first few kilometers. This is especially true for older vehicles with high mileage. But at the latest when the engine is warm, it should run smoothly.

It is not uncommon for a marten bite to be responsible for the problems. Just Exposed ignition cables or vacuum lines are often bitten by martens and can then cause the engine to run unevenly. Depending on the position, you can see this yourself by looking into the engine compartment.

In the workshop, it is first determined whether the engine is still running on all cylinders. In addition, the fault memory is read out with a diagnostic tester.

In the following you will find an overview of the common causes of problems when the engine is not running smoothly.

If you click on the linked guides, you will find more Learn about other common symptoms and costs. So you can perhaps rule out some causes.

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Motor draws in false air (also known as secondary air or external air)

For optimal fuel combustion, the mass of the air supplied must be precisely recorded and passed on to the engine control unit. Based on the determined values, this then adjusts the mixture preparation.

If there is a deviation due to additional air flowing in, the result can be that the engine runs irregularly. The following causes, among others, are possible for the false air:

A must for anyone who wants to understand their car

Did you know that all modern cars (built around 2003 or later) have a very comprehensive fault memory that you can read out yourself? You can find suitable devices at Amazon *, for example.

Last updated on May 21, 2021 at 8:53 pm. We point out that the prices displayed here may have changed in the meantime. All statements without guarantee.

Problems with the ignition system

In Otto engines, the fuel-air mixture is externally ignited by means of spark plugs. If your irregularly running engine is a gasoline engine (= "petrol"), the following causes are possible:

Fuel supply problems

In order for an engine to run optimally, the information from the engine control unit must always optimally determined fuel quantity can be correctly injected can. If there are problems with the fuel supply or the fuel injection, this can be indicated by the engine running unevenly.

Motor control problems

The engine control unit (in short: Control unit or also as ECU / engine control unit or ECM / electronic control module controls and regulates a large number of functions in modern motor vehicles that are necessary for the proper operation of the vehicle. All sensor data come together here.

If the engine control unit is defective, this can manifest itself in different ways. Sometimes the engine doesn't start at all, sometimes it “just” runs out of round. A defective control unit can often be repaired by specialist companies. This is usually much cheaper than a new part. Often the costs are around 350 euros plus removal and installation.

Electronic problems / defective sensors

The engine control is permanently dependent on a large number of measured values ​​from a wide variety of sensors. If there is a defect or a cable break, incorrect or no measured values ​​at all are transmitted to the control unit.

Incorrect measured values ​​often ensure that the engine control unit makes the theoretically required adjustments to the mixture preparation. The The result can be an uneven engine run.

Other possible causes:

TIP: Do not drive to a workshop before you have determined the current value of your vehicle. So you always know in advance exactly the cost up to which a repair is still worthwhile!

Simply use the following form from wirkaufendeinauto.de (100% free and non-binding).

Effects of a rough engine run on the main inspection

In most cases, an uneven engine run results in a failure of the main inspection, as the emission test is not passed due to the respective defect.

Do you continue to drive despite the uneven engine running?

If you notice that the engine is not running smoothly, you should visit a workshop as soon as possible and avoid long journeys.

Otherwise you risk expensive consequential damage that can lead to engine damage. This often represents an economic total loss of the vehicle.

If you notice that the engine is not running smoothly during a test drive with a used car, it is better not to buy it.

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Still unanswered questions?

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