A situation where the engine suddenly stops working at the moment of stopping before a traffic light or when gas is discharged can take even an experienced driver by surprise. This is not just discomfort, accompanied by the loss of power steering and brakes, but also a direct threat to the safety of traffic in a dense stream. Idle-deafness Often signals serious failures in the mixing system or engine control that require immediate attention.
Reasons why machine behaves in a similar way, there can be many: from banal pollution of the throttle to critical problems with the sensor of the position of the crankshaft. The driver needs to understand the physics of the process: when the engine is braking or completely stops, the engine goes into idling mode, and if the system cannot maintain steady speeds, it occurs (stop). The most common reason for abrupt stop of the engine is a critical violation of the air supply or spark at the time of transition under load to idle.
In this article, we will analyze in detail the main nodes responsible for the stability of the power unit, and determine the algorithm of actions for diagnosis. Ignoring the problem can lead to the fact that the next time the car will not start at all or the failure of the brake system will occur at high speed.
⚠️ Attention: If the engine stalls, immediately turn on the alarm and try to roll out inertia to the side of the road, as the power steering and vacuum brake booster will cease to function after 1-2 pedal presses.
Failures of the idle and throttle regulator
One of the most common reasons why car stalls when braking, is incorrect operation of the regulator of idling (RX). This actuator is responsible for the supply of air bypassing the closed throttle, ensuring stable operation of the motor without loading on the pedals. When you release the gas and squeeze the clutch or turn on the neutral, the throttle closes, and all the air enters through the RX channel.
If the regulator rod is coked with a load or completely out of order, the engine begins to “suffocate” due to lack of air. In modern systems, where the role of the RX is performed by an electronic throttle valve (E-gas), the problem often lies in the contamination of the valve itself or malfunctions in its calibration. Electronic control unit (ECU) may not have time to properly open the valve to maintain the speed, which leads to a sharp drop in RPM and stop the engine.
For diagnosis, it is often necessary to remove and wash the node with special cleaners. However, if the problem persists after cleaning, it may be necessary to replace the sensor or carry out a procedure for adapting the throttle through a diagnostic scanner.
- 🔍 Check the course of the rod RX - it should move smoothly without jamming.
- 💨 Evaluate the degree of contamination of the throttle with oily sodium.
- ⚙️ Check the integrity of the electrical chip and the wires going to the regulator.
How to clean a throttle without removing it?
There is a method of washing throttle "in place" with a spray-purifier carburetor. It is necessary to reset the negative terminal of the battery, remove the duct pipe, spray the purifier on the valve and several times manually open / close the valve. However, this method is less effective than the complete disassembly and washing of the unit, as it does not allow to clean the side channels and the regulator itself.
Cleaning the throttle and RX eliminates up to 60% of cases of spontaneous decomposition at idle speeds, if there are no other mechanical breakdowns.
Problems with the ignition system and candles
The second critical aspect is the quality of spark formation. When braking the engine in the cylinders creates a discharge, and the composition of the mixture can change. If spark-plug have an increased gap, swelling or cracks in the insulator, the breakdown of the spark can occur unstablely. This is especially noticeable in wet weather or with a sharp discharge of gas, when the load on the ignition system changes abruptly.
Do not forget about high-voltage wires, as well as the ignition module. Microcracks in the insulation of wires can lead to a leakage of current to the mass, especially when the body vibrates during braking. In engines with individual ignition coils (as in modern ones) VAG or BMW) the coil itself or its connector often fails, causing tripling and subsequent engine stoppage.
Diagnostics of the ignition system requires a visual inspection of candles for the color of the soda and checking the spark for tear. Black soda indicates a rich mixture, white - about poor or overheating, and oily - about the entry of oil into the combustion chamber through worn rings or oil caps.
Unrecorded air suction and vacuum leaks
Violation of the tightness of the intake tract is an insidious problem that often manifests itself precisely when braking. When the throttle is closed, a high discharge is created in the intake manifold. If the system has a crack in the pipe, the gasket of the collector is damaged or the ventilation hose of the crankcase jumps off, excess air rushes there.
This air is not counted. air-flower (DMRV) or absolute pressure sensor (DAD), which leads to a strong depletion of the fuel-air mixture. The ECU tries to adjust the fuel supply, but does not have time, and the engine stalls. Often such leaks are accompanied by a whistling sound when the engine is running.
Particular attention should be paid to the vacuum brake booster. Because you brake at the moment of deceleration, the vacuum membrane is under load. If there is a fistula in it or in the hose running from the collector to the vacuum machine, when pressing the brake pedal into the collector, a huge amount of air will be sucked in, instantly crashing the revolutions.
- 🌬️ Check all rubber intake system connections for elasticity and cracks.
- 🔊 Listen to the characteristic hissing when the engine is running on idles.
- 🔧 Inspect the connection of the intake manifold with the head of the cylinder block.
Failures of sensors and electronics
A modern car is controlled by a computer that relies on readings from multiple sensors. If throttle-proof (DPD) transmits incorrect data that the valve is open, although it is closed, the ECU will pour excess fuel, causing overflow and defuse. A faulty DMV behaves the same way.
The critical element is the crankshaft position sensor (CRPS). It synchronizes the work of nozzles and ignition coils. If this sensor is “heating” or has damaged wiring, it can lose signal at the time of vibration or change in temperature, which leads to instantaneous stop of the engine without the possibility of restarting before cooling.
Also worth mentioning is the knock sensor and the lambda probe. Although their malfunction is less likely to result in instantaneous stalling, (long-term incorrect readings) can knock down ECU corrections, making the mixture too poor or rich for stable idling.
| Sensor. | Symptom of malfunction | Impact on idling |
|---|---|---|
| DPKV (Kolenwala) | The engine is dead and not starting. | Total loss of synchronization |
| DMPW (Air consumption) | Floating speeds, increased consumption | Wrong calculation of mixture |
| DPDPZ (Throttle) | The snatching when dispersed, deafening when dropped | False load determination |
| Lambda probe | Black stain on candles, smell of fuel | Unstable correction of the mixture |
⚠️ Attention: If you suspect a malfunction of the DPCV do not try to start the car repeatedly in a row, this can land the battery or disable the starter.
Fuel system: pump, filter and pressure
Sufficient pressure in the fuel ramp is the key to stable engine operation. If fuel-pump The gas pump mesh is worn or clogged, the pressure may be enough to move under load, but it will not be enough to maintain idling speeds, especially after braking, when an accurate dosage is required.
A clogged fuel filter also creates flow resistance. At the moment when the engine needs to quickly react to a change in mode (the transition from load to idle), the lack of fuel leads to impoverishment of the mixture and stop. In diesel engines (Common Rail) the problem is further exacerbated by the high requirements for purity and pressure of the fuel.
Diagnosis is made by measuring the pressure in the fuel ramp with a manometer. Normal values are usually 3.0-4.0 bar for gasoline injection engines. If the pressure drops immediately after the ignition is turned off or is not kept under load, the pump or pressure regulator shall be replaced.
☑️ Diagnostics of the fuel system
Mechanical problems of the engine and timing
The most unpleasant scenario is mechanical malfunctions. The knocked-down phases of gas distribution due to the GRM belt jumping on the tooth can cause the valves to open at the wrong time. This causes claps in the intake or release and loss of power, up to stalling.
Low compression in one or more cylinders also prevents the engine from operating at low revs. Wear of the piston group, burn valves or breakdown of the gasket of the GBC - all this requires serious repair. If the machine stalls and at the same time a metal knock is heard or there is a strong vibration, it is better to stop operation.
It is also worth checking the crankcase gas ventilation system (PCV). If the PCV valve is jammed in the open position, the engine will suck in excess crankcase gases, which is equivalent to air sucking, and the motor will stall when braking.
If you have a belt drive, change the belt strictly according to the regulations. A break in the belt on most modern engines leads to flexing of the valves and expensive overhaul.
Frequently Asked Questions (FAQ)
Why does the car stop only cold when braking?
On a cold engine, the ECU enriches the mixture for warming up. If the coolant temperature sensor (TTP) is faulty and shows that the motor is already hot, enrichment does not occur, and the motor stalls due to the poor mixture. It is also possible to catch RX on cold.
The car stalls when braking and the Check Engine lights up. What do I do?
The error code must be read through the OBD-II diagnostic connector. The code will point to a specific node (for example, P0300 – ignition skips, P0171 – poor mixture). Without a code, the diagnosis will be carried out by the pumpkin method.
Can a car stop at a traffic light because of bad gasoline?
Yes, low octane or water in the fuel cause detonation and unstable combustion. ECU tries to adjust the angle of ignition advance, but with a sharp discharge of gas corrections may not be enough, and the engine will stall.
Does the car die because of a malfunctioning transmission?
Straight, rarely. However, if the hydraulic transformer does not unlock at a stop or the automatic transmission selector is defective, it can "strangle" the engine, preventing the speed from falling to normal idling values, which leads to a stop.