Idle, commonly referred to as “tickover,” is the lowest possible engine speed needed for the engine to be able to run without stalling. Engaging it causes the unit’s revs to drop practically to zero. Some drivers, however, encounter a situation in which the system begins to run roughly at idle. This seemingly harmless phenomenon can carry serious consequences for the engine, which is why it is absolutely not advisable to make light of the matter. What causes rough running at idle? There are many reasons, as you will read in the further part of this post.
Why do cars have an idle?
Idle allows the engine to overcome the internal and external resistances generated by various systems without risking the stability of its operation. Engaging the tickover supplies the unit with the minimum amount of power on which - without the fear of stalling - it can carry out basic processes such as driving the alternator or the water pump. A characteristic feature of this state is the relatively low revs that stay at a similar level - far lower than when driving even in the highest gear ratio of the gearbox.
How can you recognise rough engine running at idle and what consequences can it carry for the unit?
Rough running of the power unit at engaged tickover can be recognised, for example, by increased vibrations while stationary - the problem itself, in turn, is the result of interruptions in the engine’s operating cycle. Such a state of affairs, although it often does not raise concern, can pose a serious threat to individual parts, including the dual-mass flywheel, whose replacement is counted in thousands of zlotys. That is not all, however - leaving the issue of rough engine running unattended also contributes to the gradual degradation of other important components.
For this reason it is not advisable to make light of this phenomenon - all the more so since the cause is frequently quite simple and not very costly to fix, although not always - it happens that the fault is caused by parts whose regeneration and replacement are expensive.
Rough engine running at idle: the most common causes
Why does the engine run roughly at idle? It is not as obvious as it might seem, due to the fact that there are relatively many causes of such a state of affairs. Most often the fault lies with a faulty ignition or fuel system. Below is a list of potential culprits responsible for the engine running roughly at idle.
Air leak in the engine
This is one of the most common reasons why the engine does not run smoothly at low revs. We speak of an air leak when air getting into the cylinders is located beyond the air flow meter or the carburettor, so that the onboard computer is not able to read it. Moreover, in such a situation the intake manifold is not provided with the appropriate vacuum while stationary, which translates into the engine vibrating at idle.
Damaged ignition system
Here we are talking about faulty or worn-out spark plugs, leads and ignition coils, in other words, a failure of electrical components, because of which the engine has trouble increasing its rotational speed.
Damaged/faulty injectors
The problem concerns leaks, exceeded correction values, or worn-out injector seals. When they fail to deliver fuel to the combustion chamber, the unit will not be able to run efficiently, the result of which will be its rough operation at idle and beyond
Damaged/clogged fuel pump
this is a component whose task is to deliver fuel from the tank to the injectors. When it becomes damaged or clogged, the engine will receive too little fuel, which will manifest itself as heavy and rough running at idle.
Poor engine earth
It is essential for the proper operation of the electronics on the power unit; if it is absent, problems with the stability of the drive’s operation may appear; this problem, however, occurs relatively rarely, although it should not be completely ruled out.
Incorrect rotational speed
The norm for rotational speed at idle is taken to be from 600 to 1000 revolutions per minute - if it is lower or higher, the engine may run roughly.
Clogged fuel filter
The fuel filter is a part whose task is to trap contaminants from the fuel. Over time, however, it becomes clogged, which is why it is important to remember to replace it regularly. When the filter becomes clogged, this can lead to rough running at idle.
Damaged air flow meter
Another of the causes of rough engine running at idle can be a malfunctioning air flow meter. It is responsible for measuring the mass of air delivered to the power unit and sending this information to the computer. When it fails or becomes dirty, it will provide erroneous data, which will result in the selection of an incorrect proportion of the air-fuel mixture, which in turn will contribute to rough engine running at idle.
Dirty lambda sensor
The lambda sensor is responsible for examining the quality of the exhaust gases - or more precisely - how much air is contained in them. On the basis of the measurement it determines whether the mixture is rich or lean - as a result of becoming dirty (or damaged) the sensor is not able to assess this, which in turn will result in the selection of the wrong fuel-to-air ratio, and this in turn may translate into problems with smooth engine running at idle and beyond.
Rough running of the unit at idle - summary
Rough engine running at idle, or to use more technical terms, at tickover, although at first glance it does not herald anything serious, when ignored, can lead to serious damage to individual elements of the drivetrain and beyond. To save yourself large expenses, you should not delay and it is worth going to a car workshop for a diagnosis - the cause may be something very easy to fix that does not generate large replacement costs.
