The situation of sausage at idle speeds is familiar to many motorists, characterized by unstable powertrain operation, jiggling, body vibrations and floating revs. The driver notices that the tachometer hand gallops randomly, and the car loses traction at stops at traffic lights.
This symptom cannot be ignored because it signals a misalignment or combustion of the fuel mixture, and if the engine is sausage, one or more cylinders are not working correctly or are shut down altogether, leading to increased fuel consumption, accelerated wear and tear of parts, and the risk of sudden stoppage in flow.
In this article, we will discuss the main causes of engine instability, how to conduct your own initial diagnosis, which units to check first and when to go to the service, we will look at both gasoline and diesel units, identifying the root of the problem systematically.
Suction of unaccounted air: the enemy of stability
The most common reason an engine sausages on idles is to pump unaccounted air into the intake manifold. The engine control system (E. M. S.) calculates the amount of fuel using data from the mass air flow sensor (M. M. R. A.), and if there is a hole in the system after the sensor, excess air is sucked in there that the ECU cannot see.
As a result, the mixture becomes too-poorAnd the engine starts to work or it gets out of order, and most often, the air gets through cracked pipes, the intake manifold, or the nozzle sealing rings, and in older cars, the rubber elements dry out and lose their tightness.
You can visually check for a suction by looking at all the hoses for cracks, and a more accurate method is to use a carbcliner or a brake cleaner, and if you run the engine, spray the suction on the joints of the pipes, and if the engine speed changes, you've found the leakage site.
⚠️ Warning: Be careful when using flammable aerosols near the engine running. Avoid spraying on a hot manifold or exhaust system to avoid causing a fire.
Special attention should be paid to the vacuum brake booster, and if the membrane inside is damaged, the engine will suck air through the brake system, which is a common reason why the motor "sausage" when pressed on the brake pedal.
Ignition plugs and spark system
The second most likely cause of the instability is the problem with the ignition of the mixture. If the engine sausages, then the spark is either too weak or disappears intermittently. spark-plugNagar, increased clearance between electrodes or insulator breakdown lead to ignition failures.
Turn the candles out and look at their condition. Black soda is a rich mixture, white is poor or overheated. Oil plaque is a problem with the piston group or the oil caps. If the candles haven't changed in a long time, replacing them is the first step to solving the problem.
And high-voltage wires, too, because over time, the insulation cracks and the current starts to break through, especially in wet weather, and the ignition coils fail, and modern motors often have a coil for each cylinder, and one of them immediately causes a tripling.
You can use a multimeter to test the resistance of wires or coils to diagnose it, but the best way to do that is to eliminate it by changing the parts in turn and observing the behavior of the engine.
Fuel system: pressure and injectors
If the air and spark are in order, then the problem is the fuel supply, the engine sausages on idlers if the cylinders are not getting enough gasoline or diesel, this can be caused by clogging of the fuel filter, a malfunction of the gas pump or a loss of performance of the injectors.
Clogged injectors spray fuel unevenly, creating an irregularly shaped torch. The fuel does not burn completely, and the cylinder is intermittent. You can use special additives in the tank to clean the tank, but in advanced cases you need ultrasonic cleaning on the stand or replacement.
It is important to check the pressure in the fuel ramp. If the gas pump does not create the desired pressure (usually 3-4 atmospheres for the injector), the mixture will be poor even with serviceable injectors. The fuel pressure regulator can also pour gasoline back into the tank, preventing the system from going to operating mode.
☑️ Diagnostics of the fuel system
Fuel quality is critical, bad gasoline with water or dirt quickly disables the injection system, and if the problem occurs immediately after filling at a questionable gas station, it is better to drain the fuel and clean the system.
Idle valve and throttle valve
On mechanical throttle engines, the idling regulator (RX) is responsible for stabilizing the revs. It is a stepper motor that controls the bypass channel, bypassing the closed valve, and if the RX is contaminated or jammed, the engine stalls or snags.
The throttle also requires attention, and the throttle that settles on the edges of the throttle prevents it from closing tightly or, conversely, prevents the opening of the bypass channel, and the electronic throttle can malfunction due to a malfunctioning potentiometer of the position of the throttle.
Throttle cleaning is a simple procedure that you can do yourself: remove the tube, spray the cleaner and wipe with soft cloth. Many cars require a throttle adaptation procedure after cleaning.
| A symptom. | Possible cause | Method of decision |
|---|---|---|
| Turnovers float | Air suction | Searching for leakiness |
| Engine troit | Coil failure | Replacement of coil/candles |
| It's dead at a traffic light. | Dirty RX | Cleaning the regulator |
| High-end spending | Watering nozzles | UZ cleaning |
How to adapt the throttle valve?
The adaptation procedure depends on the brand of the car. It is usually a combination of ignition and pedal pressing in a certain time interval. For accurate data, use a diagnostic scanner or manual to your model.
If the problem persists after cleaning the valve, the valve drive motor itself or the electrical part may have failed, and only the replacement of the valve will help.
Compression and mechanical failure
When all of these systems are working and the engine is still sausage, you should think about "iron" because low compression in one of the cylinders does not allow you to create enough pressure for normal combustion of the mixture, which is a sign of wear and tear of the piston group.
Causes of compression fall:
- 🔥 The occurrence or wear of piston rings.
- 🔥 A scorching valve or a violation of the heat gap.
- 🔥 Breakdown of the gasket between the cylinders.
- 🔥 Bullies on the cylinder walls.
The compression test is done by a compressometer. The difference between cylinders by more than 1 atmosphere indicates a serious problem. If you pour some engine oil into the cylinder and the compression goes up, the rings are worn out. If it doesn't go up, there's a valve problem.
⚠️ Warning: Operating a low-compression or punched-out GBC engine can lead to overheating, piston jamming and expensive overhauls.
It is also worth checking the timing phases: if a belt or a GRM chain jumps on the tooth, the engine will run extremely unstable, lose power and can "shot" into the muffler or intake.
Sensors and Electronics: Hidden Enemies
The modern engine is controlled by a computer that receives data from a variety of sensors, and failure of one of them can cause the engine to start to “sausage”, the main suspects are the crankshaft position sensor (CRP) and the camshaft position sensor.
If the DPC fails, the ECU doesn't know when to deliver spark and fuel, it causes chaotic ignition misses, it also affects the oxygen sensor (lambda probe), if it "lies" about the exhaust gas composition, the mixture correction system works wrong.
Problems with the electronics themselves cannot be ruled out: oxidation of contacts in connectors, poor engine "mass" or malfunction of the control unit can cause phantom problems. In winter, condensation in connectors is a common cause of trimming.
Use the contact spray to treat electrical connectors, which will help eliminate oxidation and improve contact, which often solves problems with floating revs.
Computer diagnostics is the best way to detect sensor errors, and even if the Check Engine light is not on, there can be stored pending error codes in memory indicating a faulty node.
Comprehensive diagnostics DIY
So, to avoid guessing or changing details at random, stick to the algorithm: first, visual inspection for air sucking and wire integrity, then check for candles and coils, then assess the throttle status and measure compression.
If you don't have experience, start by connecting an OBD2 scanner, which will show which cylinder misses ignition (P0300-P0304 errors) and this will immediately narrow the search. If the scanner shows a rich or poor mixture, look for a sucker or a problem with the nozzles.
Remember, the engine is a system. A problem in one place can cause symptoms in another, for example, an air suction can kill a lambda probe, and you'll have to change both of those if you don't find the hole in time.
System approach and consistent check from simple to complex allow you to find the cause of unstable engine operation in 90% of cases without unnecessary costs.
Frequently Asked Questions (FAQ)
Why does the engine only work on cold?
If the engine is only trembling when warmed up, the most likely problem is the injectors (not keeping the pressure), candles (not breaking the spark on the cold) or the coolant temperature sensor (the ECU does not know that the motor is cold).
Can I drive if the engine is running?
It's not recommended. Unburned fuel gets into the catalyst, causing it to overheat and melt, and gasoline flushes the oil off the cylinder walls, accelerating the wear of the piston, and you can get to the service, but you can take care of it.
Why does the engine stop and stop when braking?
Most often, this indicates air sucking through a vacuum brake amplifier or a malfunction of the idling regulator, which does not have time to stabilize the revolutions when the gas is discharged.
How do you distinguish triplets from detonations?
Troining is the ignition gaps, the vibrations, the power loss. Detonation is the ringing metal knocking when the mixture is loaded due to premature ignition. These are different problems with different causes.