Why the engine speeds themselves rise: a full analysis of malfunctions

The situation when engine speed Spontaneously increasing without your intervention is one of the most alarming signals for any motorist. This can occur both at idle, when the tachometer arrow suddenly jumps to 1500-2000 units, and during movement, creating an effect of uncontrolled acceleration. Ignoring this behavior of the power unit is categorically impossible, as it indicates a violation of the balance of the fuel-air mixture or a failure in the engine control system.

In modern cars, complex electronics are responsible for maintaining stable operation, which reads the readings of dozens of sensors. If electronic control (ECU) gets incorrect data or cannot execute a command due to a mechanical malfunction, it goes into emergency mode or begins to randomly adjust the fuel supply. Understanding the nature of this phenomenon is the first step to safely operating a vehicle and preventing costly repairs.

Often drivers notice that the problem manifests itself only on a warmed-up engine or, conversely, only in the cold. The nature of the jumps can also be different: from a smooth build-up to sharp, convulsive jerks. In this article, we will discuss in detail the mechanical and electronic reasons why. turnover They behave unpredictablely, and how to diagnose a malfunction on their own.

Unreported air suction: the most common cause

The main reason that the revolutions rise by themselves is the ingress of excess air into the intake manifold after the mass air flow sensor (MMRV). The engine works on the principle of a pump, sucking in air, and if there is leakage in the system, the so-called so-called "pressurized" is formed. sucker. The ECU sees more air than the sensors have calculated and tries to stabilize the work by adding fuel, which leads to an increase in speed.

Most often, a leakproofness violation occurs in the joints of the pipes, where rubber seals eventually dry up and crack. Also, the culprits can be gaskets of the intake manifold, which "blown" from time and high temperatures. Even a microscopic crack in the air filter corrugated can let enough air through to knock down the settings. idle.

⚠️ Attention: Searching for air suction by ear is often ineffective, as hissing can be barely noticeable. Using a Quick Start spray or carburetor cleaner to check tightness requires extreme caution - getting liquid on hot exhaust elements can cause ignition.

For accurate diagnosis of intake mechanics, specialists use a smoke generator. This device pumps smoke into the intake manifold, and the leakage sites become visible to the naked eye - the smoke begins to come out of cracks and joints. If such equipment is not available, you can gently squeeze the pipes one by one, watching the reaction of the tachometer: if the speed is normalized when clamping a particular hose, then the problem is in this area.

Failures of the idle and throttle regulator

The idle regulator (RX) is an actuator whose task is to accurately dosage air with a closed throttle. If the valve RX is contaminated with oil soda or jammed mechanically, it ceases to properly block the air supply channel. The engine receives an excess amount of oxygen, and turnover They spontaneously grow, sometimes reaching values characteristic of the mode of operation under load.

A similar situation is observed with the electronic throttle (E-gas). In such systems, there is no separate RX, its functions are performed by the valve itself, controlled by the electric motor. The coar at the edges of the valve or wear of the gears of the drive can lead to the fact that the flap does not close to the end or, conversely, is opened by mistake by the ECU command. Cleaning the throttle with special aerosols often solves the problem, but requires subsequent adaptation It's a diagnostic scanner.

• 🔧 Pollution of the rod of the RXX or the edges of the throttle with oily soda.
• 🔧 Wear or break of the regulator electric motor winding.
• 🔧 Oxidation of contacts in the connection connector of the throttle position sensor (DPD).
• 🔧 Mechanical jamming of the drive cable (on old cars with mechanical throttle).

It is important to note that after cleaning or replacing the RXX on many modern cars (e.g., the LCD) VAG Group, BMW, Hyundai) a training procedure should be carried out. Without this, the ECU will continue to use the old corrections, and the problem of high revs will remain. The adaptation process usually takes a few minutes and is performed via the OBD-II connector.

Effect of temperature and pressure sensors on engine operation

The electronic engine control unit forms a command to open the throttle or valve RXX, based on data from sensors. If the coolant temperature sensor (TTP) transmits the wrong signal that the engine is cold, the ECU will maintain high temperatures. turnover It is also possible to warm up, even if the engine has been hot for a long time. This is a classic situation of “warm-up razor”, which is delayed due to faulty sensor.

Also critically important is the throttle position sensor (DPD). It tells the computer how hard you pressed the gas pedal. If the graphite layer has worn off inside the sensor or a track has broken, the signal can jump. ECU receives the command "driver gave gas" and raises speed, although the pedal is released. Diagnosis of such malfunctions is possible only with the help of a multimeter or an oscilloscope, tracking the smoothness of voltage changes.

Sensor.	Symptom of malfunction	Impact on turnover
DRL (Temperatures)	Excess fuel consumption, black stain on candles	Keeps high speeds as cold as it is.
DPTA (Throttle provisions)	Scuding, floating idle	Spontaneous increase in the release of the pedal
DAD (Absolute Pressure)	Power loss, detonation	Unstable idling, horse racing
Lambda probe (Oxygen)	Unstable work in all regimes	Adjustment of the mixture in both directions (rich / poor)

Special attention deserves lambda probe. If he is lazy or lying, showing constant poverty of the mixture, the ECU begins to actively add fuel and air, trying to level the composition. This can cause cyclical fluctuations in speed, when the engine then "chokes", then sharply gains speed.

How to check the SDG without a scanner?

You can remove the connector from the temperature sensor with the engine running. If the ECU goes into emergency mode and turns on the cooling fan, and the revolutions change - most likely, the sensor or its circuit is faulty. However, this method does not work on all cars.

Problems with the fuel system and nozzles

Although high revs are most often associated with air, the fuel system also contributes. If nozzle (injectors) do not hold the pressure and “pour” fuel even with closed valves, the cylinders get re-enriched mixture. To burn this excess gasoline, the engine is forced to increase the rotation frequency of the crankshaft. This condition is dangerous not only for the environment, but also for the engine itself - it is possible to wash the oil film from the walls of the cylinders.

The other extreme is low pressure in the fuel ramp due to a worn gas pump or clogged filter. ECU, seeing the lambda probe poor mixture, trying to compensate for the lack of fuel by increasing the opening time of the nozzles and increasing the speed so that the engine does not stall. In such cases, the car can twitch and stall when sharply pressed on the gas, but at idle speeds can be unstablely high.

Fuel quality plays a crucial role here. The use of gasoline with a low octane number or the presence of water in it leads to detonation and incorrect operation of the ignition system. ECU, fixing the detonation, tries to adjust the angle of ignition ahead, which can indirectly affect the stability of the engine at idle.

Electromagnetic valve adsorber and ventilation system

The gasoline vapor capture system (EVAP) is designed for the environment, but its malfunction often causes high revs. Fuel vapors from the tank are accumulated in the adsorber, and then, on the command of the ECU, are fed into the intake manifold through an electromagnetic flare for combustion. If this valve "sticks" in the open position, a mixture of gasoline and air vapors constantly enters the intake.

The engine perceives this extra volume of gases as an air sucker and tries to level off work, resulting in floating or constantly elevated turnover. A characteristic sign of malfunction of the adsorber valve is hissing when opening the lid of the gas tank (a vacuum or excessive pressure is created) and the smell of gasoline in the cabin or near the car.

• ⛽ The adsorber blow valve is constantly open.
• ⛽ The adsorber carbon filter itself is clogged (the pairs have nowhere to go).
• ⛽ The tightness of the fuel tank or lid is broken.
• ⛽ Error in the software of the ECU, which controls the purge cycle.

Diagnosis is simple: if when you turn off the hose going from the adsorber valve to the intake manifold, and its subsequent jamming, the turns come back to normal, the problem is found. It is necessary to change the valve, since its constant openness leads to re-enrichment of the mixture and failure. catalytic converter.

⚠️ Warning: It is not recommended to permanently remove the system of adsorbing fuel vapors without software shutdown (Chip tuning). Simply by jamming the system, you risk a check engine error and breaking environmental regulations, as well as creating a thinning in the tank, which will make it difficult for the pump to operate.

Specifics of automatic transmissions and climate control

Sometimes the reason for high speeds lies not in the engine, but in adjacent systems. On cars with automatic transmission (AGB) or CVT, in case of malfunction of the hydraulic transformer or solenoids, partial slippage may occur. The engine spins, trying to compensate for the loss of torque, creating the illusion of spontaneous increase in speed.

It is also worth considering the work of the climate installation. When the air conditioner is turned on, the load on the engine increases sharply. EBU increases in advance idleSo that the engine does not die from the compressor. If the pressure sensor in the air conditioning system is lying, or if the maximum performance mode ("Max AC") is turned on, the revolutions can be kept at 1000-1200 rpm, which seems an anomaly for a cold engine, but is a standard mode.

In addition, many modern cars implemented the logic of heating the catalyst. Immediately after starting the cold engine, the ECU can artificially keep high speeds and change the gas distribution phases to heat the exhaust gases faster and enter the operating environment. In this case, you should not panic - after 2-5 minutes, the turnover should fall to normal.

Frequent Questions and Answers (FAQ)

Is it dangerous to drive at a constantly high speed?

Yeah, it's dangerous. In addition to the risk of uncontrolled acceleration, prolonged operation at high speeds without load leads to engine overheating, increased fuel and oil consumption, as well as accelerated wear of the cylinder-piston group parts. In addition, it may indicate a malfunction of the brake system (wedging calipers), which is critical for safety.

Why do the velocities float and not just keep high?

Floating speeds usually indicate that the ECU is in the process of constant correction. He adds fuel (turns grow), then decreases (turns fall), trying to find a balance. This is typical of an air sucker, a faulty RX, or a dying lambda probe that cannot give a stable signal.

Can bad gasoline cause a spike in turnover?

Absolutely. A low octane number causes detonation, which is recorded by sensors. ECU begins to "strangle" the engine, resetting, then again tries to spin. Also, the water in gasoline leads to ignition misses, which is perceived by the system as a loss of power, and it compensates for this by increasing the rotation frequency.

How to Reset Mistakes to Check if the Problem Will Go Away?

Resetting errors through the removal of the battery terminal or scanner does not eliminate the physical malfunction. The turnover can be temporarily normalized until the ECU re-calculates the parameters and reveals discrepancies. To solve the problem, you need to find and eliminate the cause (suction, sensor, valve), and only then reset the adaptation.

Does air filter pollution affect revs?

A heavily clogged air filter restricts air flow, which usually leads to a drop in power and enrichment of the mixture, but rarely causes a spontaneous increase in revolutions. On the contrary, the engine will be “suffocated”. However, if the filter is installed incorrectly or damaged, and the air goes bypassing the sensor, the effect will be reversed - an increase in revolutions due to unaccounted air.