What to do if the engine speed swings when warming up?

Tips for car owners: what to do if the engine revolutions are floating during warming up

Drivers’ complaints that in all cases of heating the motor in its functioning strange things with revolutions begin to occur (the so-called “floating effect”), have to hear not so rarely. This unpleasant mishap is inherent in gasoline engines that have injection, carburetor formats, as well as engines that run on diesel fuel. If the revolutions suddenly go off when the engine heats up, it is a sure signal that the unexpected has happened to it and it is necessary to look for the cause and eliminate the malfunction without delay.

What to do if the engine revolutions are floating when heated

The reason for the floating revolutions

If the revolutions float on a warm engine on load or in idle mode, you should immediately conduct a comprehensive diagnosis of the car, so as not to aggravate the situation. But at the initial stage of research, it is advisable to understand the peculiarities of revolutions floating. An ordinary tachometer will help to fix it. If everything is normal with the engine, the tachometer will fix stable indicators of about the same level (about 800 revolutions per minute), without sharp jumps. However, if something is wrong with the engine, the range of tachometer readings will rapidly increase, making from 500 to 1500 revolutions per minute.

The presence of revolutions floating also proves the size of engine roar, which from time to time rises and falls. In addition, the engine vibrations of different strengths, changing in a sinusoidal manner, can be distinctly felt in the automobile cabin. Such mishaps most often are fixed at unstable revolutions of the engine, which operates in idle mode.

However, tachometer “jumps” are sometimes observed during intermediate engine revolutions, which is inherent to diesel engines. At deviations from the norm, the tachometer can show an absolutely inconceivable range of revolutions. For example, from 500 to 1000 and then to 1500 revolutions per minute, after which they rapidly drop, in reverse order, to 500 revolutions. This is clearly noticeable when the engine builds up a load:

  • after the brake pedal is depressed;
  • turning the power steering wheel;
  • the air conditioner is on;
  • during transient driving and so on.

In such cases, the engine at idle when there is no extra load manages to keep the RPM stable, but as soon as it appears, the RPM immediately falls and the engine almost shuts down. Unreasonable increase of fuel consumption and other factors are considered as additional “leads”.

The presence of floating revolutions of the engine

Methods of solving the problem

Having detected floating revolutions, experienced drivers proceed to check the relevant electronics. During diagnostics, special attention is paid to the throttle assembly, as well as sensors and actuators. Other mechanisms also need to be diagnosed, including the ignition system and idle speed regulator, as well as air, fuel filter, injector nozzles, etc. The air flow regulator and the air flow sensor are especially troublesome. After a thorough diagnosis, it often turns out that the entire cause is a heavily contaminated throttle valve, which for this reason does not close as it should, or mechanical damage to the throttle. In the first case, a careful cleaning of the choke immediately gives a positive result, and in the second case, it is best to replace the choke with a new one.

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Besides, it is worth checking the car crankcase ventilation valve, because its failure can also be connected with floating revolutions. After warming up the engine revolutions are floating and because of such, at first sight, trifle, as presence of rust on fuel injection unit blades. This often occurs when the car has not been operated for a long time, remaining in the garage. In carburetor engines, a frequent cause of floating revolutions are knocked out settings, carburetor adjustment, carburetor electrovalve malfunctions, jamming of jets, some other factors. Therefore the integral conclusion from all stated is unambiguous: it is necessary to carry out a comprehensive diagnostics of the automobile engine with the use of effective devices and experienced specialists.

The sensor of the tailpipe

The cause of the deviation of the engine operation from the normal parameters may also be a malfunction of the idle stroke regulator sensor (IAC). The whole point is that in cars, as a rule, it is not supplemented by a self-monitoring system, so onboard computers or check-engines do not signal about its breakdown. However, floating revolutions – one of the key signs of malfunction of the VTC sensor, so it needs a thorough inspection and, if necessary, its repair or even replacement, especially since its cost is relatively low.

VCF sensor

The symptoms of throttle position sensor (TPS) failure are largely similar to the symptoms of the PCB sensor failure. However, when the throttle position sensor fails, there will be a signal from the onboard computer or check engine.

Throttle valve

As mentioned above, the increased idle speed of the car on a warm engine may be a consequence of the fact that the throttle valve is contaminated. The dirt accumulated on it with time does not allow it to close freely, fully, as it is foreseen, therefore it must be thoroughly cleaned. At the same time, some drivers note with surprise, that sometimes even thorough cleaning of a choke together with idling valve is not enough. Thus, the engine still maintains high revolutions, and the brake pedal loses its elasticity, becoming very rigid. Then, according to the experts’ opinion, we have to take up cleaning of VVTi valve. There are also recommendations to flush the idle valve.

Throttle valve

Engine temperature sensor

The following situation also happens: after several years of operation of the car, it suddenly begins to have irregular rpm. They rise sharply, then immediately rapidly fall. After the car is warmed up, such jumps disappear, but only until the next engine start, after which they repeat, and with an increasing effect. As a result, the cause is a defect in the engine temperature sensor. In such cases it is best to replace it with a new one.

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Practicing drivers also note such an often occurring cause of floating revolutions, as a defect in the exhaust manifold. Most likely, a crack has formed in it for various reasons, or a gasket has failed. As a result, when the engine is running, you get a leak, and some of the exhaust gases could get into the oxygen manifold, resulting in unauthorized “jumping” of the motor.

Electronic control unit

According to expert observations, the phenomenon of floating revolutions at idle is most often inherent in injector-type engines, in which the idle speed is responsible for the “fixed” for it regulators – electronic control units of the engine. They are designed to constantly analyze the data on the functioning of idling, and in case of failures – to give the appropriate mechanisms a command to correct errors. Therefore, the cause of the occurrence of floating revolutions is often a breakdown in the electronics.

Faults in electronics

Having detected the effect of floating revolutions in a car, the driver should treat it with all seriousness so that the situation would not worsen and lead to a serious engine failure, and its large-scale repair, as is known, is always not cheap. Therefore it is better to make a thorough diagnostics of your car, and if during its process it will be found out exactly what part or block is out of order – to replace them with new ones, after which the engine will work normally.

When the engine heats up, the revolutions are floating: causes, diagnosis and repair

Tachometer with floating revolutions

The problem when the revolutions are floating on the warmed up engine, is peculiar in the first place for carbureted ICE and gasoline injectors. However, in recent years, such a malfunction is beginning to appear more often in diesel engines.

Attention: if the revolutions begin to float when idling or under the influence of a small load, it is an alarm bell, indicating a malfunction in the car. Therefore, it is necessary to carry out diagnostic measures as soon as possible to determine the location of the breakdown.

It will be useful for any owner of the vehicle to know for what reason the revolutions may float on a warm engine, what is the danger to expensive parts, as well as possible symptoms to determine the improper operation of the car.

Characteristic symptoms of a breakdown

First of all, the tachometer will help to determine the breakdown. It is possible to see the occurring malfunction even at idle. In normal operation, even a slightly warmed up engine at idle will keep the usual indicator on the tachometer – 800 rpm.

The situation may change only when the idle RPM is warmed up. In this case, the revolutions rise independently by ECU in the range of 1000 – 1100. When the ICE temperature starts to increase slightly, the unit independently lowers the idle RPM indicator to the 800 mark.

If there is a problem with the engine operation, the RPM value will start to drop drastically and then increase again (for example, at first the indicator can drop sharply to 500, and then increase to 800 or higher at the same minute, and then drop sharply again).

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Sometimes you can see the jumping phenomena when the load on the engine is increased. Floating revolutions are noticed when driving in transient mode. If there is no additional load on the engine, it is able to maintain a stable RPM indicator. But when at least a small load appears, the indicators begin to drop rapidly.

If the driver does not have a tachometer, it is possible to determine the presence of floating revolutions through the occurrence of a specific sound. Since the internal combustion engine makes the same sounds and noises at a stable load, when it changes, acceleration may fail, vibration also changes. Sometimes there is a situation when the engine starts to stall.

Another no less characteristic sign is an increase in fuel consumption, the injectivity of the motor changes, sags or jerks in acceleration are observed.

Causes of appearance

When the main symptomatology has been established, it is necessary to understand why the revolutions begin to float on a warm engine. It is worth noting that such a problem is more often observed in injector engines. This is due to the fact that the responsible for the occurrence of floating revolutions is the EDMS, a complex system in terms of design and operation.

It contains a special controller, actuating equipment and sensors. The control unit receives signals from sensors, which transmit information to the executive equipment. As a result, it maintains stable engine rpm at idle and other modes, regardless of what mode the engine continues to run.

Regardless of what kind of malfunction occurs, there will be air and fuel outages. There may be irregularities related to the composition of the air/fuel mixture. Mechanical damage may also cause floating revolutions.

Diagnostic measures should start with the throttle assembly, actuator and sensors. It is also necessary to conduct a comprehensive check of the ignition system, idle speed regulator and DMRV. It is necessary to understand in what functional state are the injector injectors, as well as the air filters.

– From a practical standpoint, it is not uncommon for drivers to encounter problems caused by the idle speed regulator. In fact, it is an electric motor equipped with a cone-shaped shutoff needle. If the throttle damper is closed, air begins to bypass the channel blocked by the needle;

If a technical failure occurs, the ECU can no longer pick up the mixture composition at idle, causing the rpm to start floating.

– It is equally important to pay attention to the sensor responsible for the mass flow rate. During operation, the device may be heavily contaminated, or a technical malfunction occurs;

As a result, the ECU stops receiving correct information, due to which there are spikes in the revolutions in the combustion engine and violations in the formation of the mixture.

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– Sometimes the cause of floating revolutions is severe contamination of the throttle, deformation of the structure, mechanical damage. Sometimes the construction starts to wedge, so it does not close completely;

It is possible to cope with such a failure yourself. It is enough to periodically do cleaning of the damper. After cleaning, some TCs need additional throttle training.

– In the process of diagnostic measures it will be necessary to do a check of the vent valves. During normal operation, the gases are routed to the starter, where fuel and air are mixed. Afterburning occurs in the cylinders;

As the engine wears down, the amount of accumulated gases begins to increase. When the amount begins to increase, there is a disturbance in the composition of the mixture if the valve begins to wedge. Such a disturbance also results in floating rpm.

– Speaking of carbureted engines, more often than not, floating revolutions are observed due to a failure in settings or adjustments. In addition, there is always the possibility that the solenoid valve has failed, or the no-load nozzle responsible for the idle stroke is clogged.

It is not uncommon for such a breakdown to result in the appearance of corrosion on the fuel injection unit blades. This is due to the fact that water gradually begins to accumulate in the diesel fuel.

Throttle valve, needing cleaning

What mechanisms are responsible for performance

The system consists of several mechanisms, without which normal vehicle operation is impossible:

– RCA (idle speed regulator). The design is installed in the throttle valve. It helps to regulate the cross-section of the bypass channel. It is routed past the throttle, which helps regulate the concentration of the supplied air, which is then sent to the cylinders. At the same time, the flaps remain in the closed position. Regarding the design features, it is an electric motor on which the valve is located on the rod. Through the RCA, it is possible to compensate the load, which will gradually increase and put pressure on the engine.

It is worth noting that modern manufacturers in the manufacture of electronic engine control systems are practically not equipped with the BCD. This function is performed by the throttle valve.

– The throttle valve, equipped with an electric drive. It helps reduce or increase the volume of air passing through;

– valves that help open the ducts to further enrich the mixture with oxygen and maintain the rpm for warming up. Most commonly found on Japanese-made vehicles.

Help and advice from the experts

Before going to the technical center, you can try to cope with the breakdown on your own. An unqualified specialist is able to cope with the following types of breakdowns:

– It was previously discussed that excessive air suction can cause the air conditioner to spike. To avoid such malfunctions and breakdowns, the first thing to do is to check if the sealing of the system that is responsible for transporting the air is okay. To do this, simply remove the hose, connect it to the compressor and start the oxygen supply. Lower the hose into a container filled with water. This method will help check for deformations and cracks;

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– To check the idle stroke regulator, you must use a multimeter to determine if there is resistance. In the case of a reading in the range of 40-80 ohms, you can conclude that the device is out of order;

– another diagnostic method can be used. This will require cleaning the vent valve, where a large amount of crankcase gases accumulate. The structure is removed and washed with a special composition designed for carburetors. As an alternative, kerosene can be used. This will help eliminate dirt and dust from the valve;

– the ECU sensors. In this case, there is no point in making repairs. If the sensor is in disrepair, it is easier to buy a new one. This will help to save on material and time costs;

– If the motorist has no experience in interacting with the throttle valve, then the flushing and cleaning should be entrusted to real professionals. If you do not need to remove the choke, it is possible to cope on your own: disconnect the hoses, inject a special cleaner into the throttle;

The most important thing is to be sure to deactivate the choke from power. It is worth noting that on most cars, the choke is heavily fouled. You will need to choose the gap correctly beforehand, or use specialized equipment.

– On a car with a carburetor, first adjust the stroke at idle. Sometimes it is necessary to clean the nipple. To cope with the task, you may only need to inject a special composition or aerosol, and then blow the structure with compressed air.

Eliminate corrosion or just beginning to rust from the fuel injector can be done with a specialized cleaner. As a rule, it should be poured into the fuel tank. Some specialists say that such cleaner may be even poured into the engine oil in small quantities.

Adjust engine RPM

According to drivers, in this way it is possible to prolong the life of the pump from the occurrence of rust, as well as as a preventive measure. However, it is strongly not recommended to use such a method for specialized construction equipment or on diesel engines.

In fact, there are many conditions that contribute to the appearance of floating revolutions. Such situations can occur both on a cold and hot engine, in idle mode or in other transient modes.

If a malfunction occurs, it should not be ignored. On the contrary, it is important to find a suitable solution as quickly as possible. Otherwise, sooner or later the engine will fail, the probability of accidents is high. Also, the driver will have to spend more money to buy new components.

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