An irregular idle speed or unexpected engine stalling in the Volvo S90 often points to problems with the throttle body, fuel pump, or even cylinder head overhaul. These issues frequently occur for Volvo S90 owners and lead to unpleasant situations while idling or in traffic. This article provides concrete information on the causes, symptoms, and solutions. As an owner, you should be familiar with these.
What exactly does idling mean?
Idling means that the engine is running without you pressing the accelerator or the vehicle moving. The engine continues to run at a low speed to power systems such as heating, cooling, and electronics. This process consumes fuel and is relatively polluting, which is why it is avoided as much as possible in modern vehicles.
In the Volvo S90, idling leads to automatic engine shutdown after approximately 2.5 minutes. This happens when the car meets emission guidelines. This feature is intended to reduce fuel consumption and emissions, but can be annoying in winter if you want to keep the engine warm. In some cases, the manufacturer adjusts this via the settings. This is done according to the manufacturer’s specifications.
‘ This can have various causes that you should investigate to prevent further damage. ’
Irregular engine idle in the Volvo S90
An irregular idle speed is a common issue with the Volvo S90. For example, the idle speed may fluctuate between 500 and 1000 rpm. The engine then vibrates noticeably or even cuts out. This can have various causes that you should investigate to prevent further damage.
Throttle body contamination and failure
The throttle body is a component that regulates the amount of air entering the engine. In the Volvo S90, the throttle body can become contaminated by soot deposits and oil mist from the air intake. As a result, the valve no longer responds correctly to control signals from the engine. This leads to an irregular idle speed or sudden engine stalling.
Solution: thoroughly clean the throttle body with a special cleaner designed for this component. Some owners report that removing fuse 23 (5A) under the bonnet for 10 minutes resets the engine computer. The engine computer is the electronic control system of the engine. After replacing the fuse, the engine relearns its idle values. This happens during a short test drive.
Vacuum leak in the brake booster
A vacuum leak occurs when air is unintentionally sucked into the engine’s vacuum system. In the Volvo S90, this often occurs in the brake booster. This causes vibrations while idling. These vibrations become stronger during braking. The engine then demands extra vacuum.
Solution: check the vacuum hose between the brake booster and the intake manifold for cracks or loose connections. Replace damaged hoses immediately to fix the vacuum leak and reduce vibrations.
Engine mount and vibrations
Vibrations at idle can also be caused by a torn engine mount. These cracks are often invisible to the naked eye. They only become apparent when the engine is under load. Use a screwdriver to carefully apply pressure to the engine while it is running. Cracks in the rubber then become visible.
Solution: replace damaged engine mounts to eliminate vibrations. This also prevents additional wear on other engine components. Excessive vibrations put a strain on these parts.
Recognising a faulty fuel pump in the Volvo S90
A failing fuel pump delivers insufficient fuel to the engine. This is particularly noticeable at idle. The engine then struggles to maintain a stable idle speed and even stalls while idling or at low speed.
Symptoms of a faulty fuel pump
Recognise a faulty fuel pump by the following signs:
- Engine stalls while stationary or at traffic lights
- Difficulty starting. This happens especially after standing idle for a long period.
- Power loss during acceleration
- Audible hissing or whistling sound from the fuel tank
- Irregular idle speed. The engine speed does not respond to acceleration.
Solution: have the fuel pressure checked by a specialist with a diagnostic tool. A Volvo S90 must maintain a specific fuel pressure. This depends on the engine type. If the pressure is too low, the fuel pump must be replaced. This component is usually located inside the fuel tank and requires specialised knowledge for replacement.
Cylinder head overhaul necessary for the Volvo S90
A cylinder head overhaul is a major repair. The cylinder head is disassembled and cleaned. If necessary, the head is skimmed. In the Volvo S90, a damaged head gasket or distorted cylinder head causes a loss of compression. This manifests itself in poor idle speed, smoke production, and coolant loss.
Signs for cylinder head overhaul
Recognise the need for a cylinder head overhaul from these symptoms:
- White smoke from the exhaust, indicating coolant burning
- Oil in the cooling system or vice-versa
- Overheating of the engine without a clear cause
- Power loss and irregular idle speed
- Engine is difficult to start or runs irregularly
Costs of a cylinder head overhaul for the Volvo S90
A cylinder head overhaul is a costly repair. The costs depend on the engine type and the extent of the damage. They are usually between 2000 and 4000 euros. This includes disassembly and new gaskets. Skimming or replacing the head and reinstallation are also included. In case of severe damage to the cylinder head, replacement is necessary. This increases the costs further.
If you suspect head gasket problems, have a compression test performed immediately. This prevents further damage to the engine that could lead to even higher repair costs.
Additional checkpoints for the chassis and suspension
In addition to engine problems, chassis and suspension issues also contribute to unwanted behaviour during idling. Therefore, test your Volvo S90 regularly on cobbles or uneven surfaces. This allows you to detect play in the suspension.
Check these components
- Control arm bushings and control arm ball joints (connections between the wheels and the chassis) for play
- Stabiliser link ends (connection points of the stabiliser bar) for wear
- Shock absorbers for leaks and performance
- Wheel bearing play while driving
Wear in these components causes extra vibrations. The body transmits these vibrations to the cabin. Combined with engine problems, this intensifies the vibrations while stationary.
Preventive maintenance for a stable idle speed
Regular maintenance prevents many problems with the idle speed of your Volvo S90. Perform simple checks and replacements. This keeps the engine in optimal condition.
Follow these maintenance tips:
- Clean the throttle body every 50,000 kilometres or at the first signs of irregular idle speed
- Replace air filters according to the maintenance schedule to minimise throttle body contamination
- Check vacuum hoses annually for cracks and hardening
- Test fuel pressure during regular maintenance services
- Monitor coolant levels and check for unexplained loss
- Have vibrations or irregularities investigated immediately. This prevents serious damage.
By acting proactively, you prevent costly repairs and keep the driving comfort of your Volvo S90 at a high level.
When should you seek professional help?
You can solve some idling problems yourself. For more complex faults, professional diagnosis is necessary. Consult a Volvo specialist if you experience persistent vibrations after cleaning the throttle body. Also, consult a specialist in the event of power loss combined with smoke from the exhaust. Do the same in the event of unexplained coolant loss.
A specialist has diagnostic equipment. This equipment reads fault codes and measures engine parameters. This saves time and prevents unnecessary replacement of components. These components are not faulty. If you suspect a cylinder head overhaul is needed, professional assessment is always mandatory. This repair is complex and costly.
On the Carnews website, you will find much more information about common problems with various Volvo models. You will also find maintenance tips. In addition, you can read about the experiences of other owners. Discover more articles about your car and stay up to date with the latest developments in the automotive world.
Frequently Asked Questions
Prolonged idling increases fuel consumption because the engine is constantly consuming fuel without the car moving or doing useful work. Furthermore, this causes extra wear and contamination of components such as the throttle body, and it can increase the likelihood of issues like irregular idling, vibrations, and engine stalling. Modern Volvos, including the S90, also often feature a function that automatically shuts down the engine after it has been idling for a certain period to limit emissions and unnecessary consumption. It is therefore recommended to keep idling to a minimum.
The start-stop system in the Volvo S90 automatically switches off the engine while stationary, which prevents unnecessary idling and reduces fuel consumption. This increases the car’s overall efficiency, especially in city traffic with frequent stops. Because less fuel is consumed, CO2 emissions and other exhaust gases are also reduced. As a result, the system contributes to a lower environmental impact and cleaner air in urban areas.
The Volvo S90’s start-stop system is designed so that the starter motor and battery are reinforced and adapted for frequent starting and stopping. Therefore, normal, frequent use does not, in principle, lead to excessive extra wear compared to the original design. However, with many short trips and frequent stop-and-go traffic, the battery can age faster, especially if it is not regularly fully charged. In practice, however, the system has been tested for this usage pattern and extra wear is kept within normal margins.
No specific, official guidelines have been found indicating when a Volvo S90’s start-stop system should be switched off manually. In practice, drivers often switch off the system in situations where comfort or continuously running auxiliary systems are important, such as in extremely cold or hot weather conditions. Furthermore, it is sometimes switched off during very short stops in succession (traffic jams, busy city traffic) to avoid unnecessary frequent starting and stopping. For exact recommendations, Volvo generally refers to the owner’s manual for the specific model and engine variant.
The Volvo S90’s start-stop system works smoothly thanks to a powerful starter motor and an upgraded battery specially designed for frequent starting and high loads. In addition, advanced engine management software and sensors (such as for brake, clutch, engine, and outside temperature) ensure that the engine only shuts down and restarts when it is safe and comfortable to do so. Integration with other systems, such as climate control and power steering/brakes, also prevents comfort or safety features from failing when the engine is off. This keeps the transition between driving, stopping, and moving off again almost imperceptible to the driver.