The internal combustion engine, whether gasoline or diesel, will definitely vibrate during operation. Therefore, the unit is mounted on the car frame on special supports (cushions) that dampen all the mechanism's vibrations and prevent them from spreading to the body. If the engine vibration at idle is felt in the cabin, then it is time to consider repairs.
Normal indicators and deviations
The principle of operation of the internal combustion engine (ICE) consists of the movement of pistons in the cylinder sleeves as a result of fuel detonation. Small explosions in a certain order cause the crankshaft to rotate, along with the pump, generator, wheels (through the transmission during driving). The transmission of torque is accompanied by the shaking of all components. All vibrations inside and around the unit are dampened by cushions.
Vibration at idle should not be transmitted to the body or cabin. Depending on the brand and model, a running engine at idle rotates at a frequency of 800-1000 revolutions per minute. But even if you press the accelerator pedal to the floor and increase the number of revolutions to the maximum value (above 5000), inside you should only hear the roar and no shaking of the steering wheel or dashboard.
A signal that a malfunction is hidden under the hood will be vibration in the cabin at idle in any weather. The reasons for this phenomenon can be different, but they are almost always characteristic of all cars regardless of the manufacturer and year of production. If the car shakes at idle, it is either due to a disruption in the normal operation of the ICE or a structural failure. Increased vibration of the power unit is caused by factors such as:
- Worn-out support
- Dysfunction of the fuel delivery system
- Faults in the air intake system
- Critical degree of wear of the timing belt
Some of the above breakdowns can be detected and fixed independently, while other issues can only be resolved at an auto repair shop.
Worn-out support
This mounting element performs three functions simultaneously. Firstly, it fixes the unit on the frame. Secondly, it dampens the vibrations from its detonations. And thirdly, it protects against impacts and jolts when driving over bumps and off-road. Therefore, the support fastening must consist of a metal frame and various damping components. There are different types of fasteners:
- Rubber-metal – the cheapest and consist of two metal plates with wear-resistant rubber between them
- Polyurethane – structurally similar to the previous ones, but polymers and synthetic rubber are used instead of rubber
- Hydraulic – the most expensive modern and adaptive fastening devices, the rigidity of which can be adjusted from the cabin depending on road conditions
Engine vibration at low speeds, when accelerating or driving uphill, is completely dampened by cushions and not transmitted to other parts. To diagnose problems with fasteners, it is enough to simply listen. If the engine runs smoothly in the parking lot, and the tachometer needle stays steadily at 800-1000 rpm, but the steering wheel vibrates, then the problem is likely with the fastening.
When these signals occur, it is better to go to a mechanic immediately. A worn-out cushion causes deformation of the unit and associated parts, which can lead to much more serious problems than just discomfort from the engine shaking at idle. In the case of damage to one or more fasteners, the engine changes its position on the frame, lowering down. This leads to deformation of the cooling system pipes, damage to covers, and other parts.
Unstable engine operation at idle
A gasoline or diesel engine operates strictly cyclically and most often in four strokes. Engine vibration at idle and at speed is caused by explosions in the combustion chambers. A fuel mixture is supplied, which is compressed by the piston. In modern vehicles, gasoline is fed directly into the chamber, where it mixes with air. Older models have carburetors where the mixing of fuel and oxygen takes place. The spark plug ignites the compressed space, the composition detonates, and pushes the connecting rod back. In a diesel engine, diesel fuel is injected into the compressed atmospheric gas, resulting in ignition and the connecting rod rotating the crankshaft.
If strong engine vibration is felt on the body and in the cabin immediately after starting, this indicates a sequence failure. The failure of a component of the fuel system has caused the malfunction. The reasons for engine vibration can be:
- No spark in the gasoline engine
- Injectors produce uneven injection
- Clogging of filter materials
- Old timing belt
- Malfunction of the mass airflow sensor
These malfunctions are the most common causes of unstable engine operation at idle.
Lack of spark
Electric current from the battery is supplied to the starter, then to the distributor, and through high-voltage wires to the spark plugs. From them, a spark is emitted during the compression stage, which ignites the fuel. Since the compression of each cylinder occurs in a certain order, the spark is formed in a similar order. If wear occurs, the contact point is charred, or the spark plug simply burns out, then there will be no detonation in the corresponding cylinder. Instead of 4 chambers, only 3 operate, and this is the reason for engine vibration. This phenomenon is called misfiring.
It is very easy to fix this issue – replace the faulty spark plug with a working one. And be sure to check the high-voltage wires. This procedure is quick and does not require special skills or finances. If changing the cables does not have the desired effect and the engine vibration at idle persists, then it is necessary to move on to other parts.
Fuel delivery
Each cylinder is connected to injectors that spray gasoline or diesel fuel in a metered manner. If they are clogged with soot, combustion products, oil, and other deposits, the fuel dosage is disrupted. There is not enough energy from the detonation to push the connecting rod at the required speed, and the order changes. Vibration of a diesel engine at idle, as well as a gasoline engine, is eliminated by cleaning or replacing the component.
In addition, it is advisable to remove contamination in the throttle valve. The market offers many cleaners, and original parts for any model can be found at an auto salvage yard. If these manipulations do not help, then the problem should be sought further up the line.
Clogged filters
Atmospheric air is extremely necessary for ignition. And it must be clean. Therefore, before entering the engine, the gas mixture passes through an air filter, where dust and other impurities are removed. Naturally, all this settles inside the filter material and reduces the permeability. The vehicle's maintenance schedule includes replacing the consumable every 25-45 thousand km. This procedure is quite simple and can be done even without a garage.
However, not only a clogged filter can cause insufficient oxygen to enter the combustion chambers and lead to car vibration. Atmospheric oxygen is supplied through practically airtight channels. If a crack or hole forms along the way, gases will escape from there. Some cars use a vacuum hose to reduce exhaust pressure in the crankcase. Loss of airtightness (cracks in the housing, detachment of the pipe) or clogging of this tube plays a role in the normal operation of the unit. Installing a new vacuum hose or restoring the airtightness of the old one instantly solves the problem.
The situation is more complicated with the filter on the fuel supply lines. If the car shakes at idle, its condition should be checked along with other elements. Gasoline and diesel fuel contain various microscopic solid objects that clog the mesh, and the petroleum product goes to the injectors in insufficient quantities. This can happen with one cylinder or all at once. As a result, the engine vibrates or stalls. To avoid unpleasant moments, it is necessary to monitor the mileage and timely replace consumables.
Wear of the timing belt/chain
The gas distribution mechanism is responsible for timely intake of oxygen and exhaust of spent exhaust gases and moves the valves. It can be single- (SOHC) or double-shaft (DOHC). The rotation of the shafts is carried out from the crankshaft through a belt or chain. This is a complex and precisely adjusted device that is responsible for two working strokes of the power unit at once. Therefore, malfunctions in it are a likely cause of engine vibrations.
Belt and chain drives must be tensioned to a certain level. Weak tension is a consequence of factors such as:
- The tensioner roller is not tight enough, so the links slip
- The belt drive is worn out due to long-term use
- Ingress of foreign working fluids (for example, after the reconstruction of another section), after which the characteristics have weakened
- Partial damage to the connecting device
If the engine shakes at idle due to these failures, it is better not to delay with repairs. A break is considered the most serious damage to the unit. Subsequently, this means expensive restoration of the iron horse.
The procedure involves installing a new water pump and tensioner roller. The repair is expensive but allows you to preserve both the engine and all components of the cooling infrastructure and gas distribution mechanism. As a pleasant bonus, the vibration in the cabin at idle will be eliminated.
Electronics
The correct proportions of the fuel-air mixture are programmed into the car's onboard computer. The amount of fuel and oxygen is controlled by corresponding sensors. If all parts are in good condition, the spark plugs are intact and new, and a slight engine vibration is felt on the steering wheel and instrument panel, then the problem is with the electronics. Malfunctioning sensors are accompanied by the Check Engine light. A worn-out mass airflow sensor cannot be restored. Only replacement solves the situation.
This is the reason why the engine starts to vibrate specifically at idle, which is the rarest occurrence. During driving, oxygen is supplied when the accelerator pedal is pressed, and the RPM is consistently above 1000-1100 units per minute, so the shaking under the hood is not felt. Replacing this component can be done independently.
How to eliminate engine vibration
Some malfunctions can be repaired independently and without a garage. Installing a sensor, spark plugs, vacuum hose, and filter elements does not require special tools – a few wrenches and a screwdriver are enough. Issues with the belt/chain and injectors are better left to professionals, as the risk of error is too high, and its consequences are catastrophic.
It is important to remember that vibration at idle, spreading throughout the car body, is not just discomfort. It is a signal that something is wrong with the iron horse, and losing days is highly undesirable. The exact source of the vibrations and why they occurred can only be determined through careful diagnostics at an auto repair shop. Professionals will quickly find and eliminate the malfunction.
