Understanding why engines stall
An engine stall occurs when the engine suddenly stops without warning, commonly resulting in the vehicle losing power steering and braking assistance. There are several systems that work together to enable an engine to run, including fuel delivery, air signal from the air intake, ignition, and the operation of the vehicle’s computer system, as well as its sensors.
When a failure, or intermittent failure, occurs in any one of the systems, control is lost and the engine will stall suddenly and completely. For example, poor idle control means the engine cannot maintain its running speed at lower RPMs, or the fuel is momentarily restricted due to a weak fuel pump or a clogged fuel filter, preventing fuel from being burned.
Sensor failures can cause the engine computer to be misled, resulting in timing changes or alterations to the fuel ratio balance. If you experience stalling more than a few times, it is likely that something is seriously wrong and professional help may be necessary to diagnose and repair the issue.
Recognising the signs of stalling and tracing the underlying problem can help you get back on the road safely.
Common causes of frequent engine stalling
If your car’s engine is stalling, it is likely due to issues with one or more of your vehicle's systems. Here, we will discuss the most likely causes of stalls and how each cause will affect your vehicle's performance.
Faulty Idle Air Control (IAC) Valve
A faulty IAC valve can be a major cause of engine stalling, particularly when the vehicle is idling or decelerating. The IAC controls the airflow into the engine to maintain a consistent idle speed. If it is clogged, stuck, or electronically faulty, the engine does not get sufficient airflow to operate normally, resulting in frequent stalling, especially when stopped, or shifting from "Park" to "Drive".
Clogged fuel filter or weak fuel pump
Fuel filters and pumps are key components in ensuring the engine has a consistent fuel flow. Filters will collect dirt and debris over time, restricting the flow, and pumps will wear down as time passes, losing pressure. Without adequate flow and pressure, engine combustion is poor, leading to hesitations and frequent stalling, especially under acceleration or while driving uphill.
Dirty or failing mass air flow (MAF) sensor
The Mass Airflow (MAF) sensor measures the amount of air entering a vehicle's engine, enabling the car's computer to accurately determine, in real-time, the amount of fuel to deliver. A faulty or dirty MAF sensor will not provide accurate readings to the computer, resulting in an air-fuel mixture that is either lean or rich. An air-fuel mixture that is either too lean or too rich can cause the engine to hesitate, misfire or stall, especially after a cold start or rapid changes in speed.
Malfunctioning oxygen (O₂) sensor
The oxygen sensors measure the exhaust gases and assist in creating a normal fuel map for effective power. Once an O₂ sensor has stopped functioning, the engine computer will not trim the fuel correctly, causing rough running or stalling under variable driving conditions. Replacing a failed sensor is crucial for maintaining optimal emissions and engine performance.
Vacuum leaks
All engines utilise a series of vacuum hoses to maintain pressure balance. Cracks in any of the vacuum hoses, gaskets, or loose intake connections can lead to a leak, which disrupts the air-fuel ratio, resulting in a rough idle and loss of power. Signs of a vacuum leak might include hissing noises, poor acceleration, and erratic idle behaviour.
Ignition system problems
Weak or faulty ignition components can cause intermittent firing or misfires, resulting in decreased combustion efficiency. Worn spark plugs, oxidised ignition wires, or failing coils will cause engine misfires and stalling, especially under load. Regular inspections and prompt replacement will mitigate these concerns.
Exhaust gas recirculation valve failure
The EGR valve recirculates a portion of the exhaust gas back into the combustion chamber, promoting cleaner combustion. The valve may become clogged, either open or closed, due to carbon buildup, which affects the air intake and causes a rough idle and stalling. Cleaning and/or replacing the EGR valve should restore proper air movement in the engine.
Bad crankshaft position sensors
Position sensors provide real-time position data on any of the engine components, which is especially critical for the timing of spark and fuel injection. Faulty or intermittent failure will mislead the engine control unit, causing the engine to stall randomly or fail to start. Diagnostic testing will isolate the bad sensors and verify a stable engine.
What to do when your car keeps stalling
Stalling unexpectedly can be a stressful event, but utilising a logical process can keep you safe while quickly narrowing down the problem.
Stay calm and pull over safely
If the engine has indeed stalled, safely and calmly guide your car to the side of the road. Turn on the hazard lights to keep you visible and to alert any driver behind you that your car has an issue.
Put the vehicle into "Park" or "Neutral"
Once you are safely stopped, put the gearbox into "Park" or "Neutral" and attempt to restart the engine. Putting the car into neutral or park keeps it from rolling, and gives the engine a chance to re-engage smoothly
Check the dashboard warning lights
Take note of any warning lights that remain present at startup. The lights that say “Check Engine”, oil, or battery, for instance, usually signify a specific area of concern that needs further diagnosis
Look for obvious issues
Open the bonnet and check for loose battery terminals, cracked vacuum hoses or low fuel. Sometimes, a temporary stalling issue can be rectified with a simple adjustment, such as re-tightening or reconnecting a cable
Do not continue to rev the engine repeatedly
If it does restart, do not rev it significantly or accelerate rapidly. Doing so can damage internal parts or cover up other problems that will make the repairs that much more difficult and expensive later on
Get an OBD-II scanner
Most modern cars will have stored fault codes that record the stall event when it occurred. You can pull that code using an OBD-II diagnostic scanner, which will help you troubleshoot the engine's issue and advise the mechanic on what to investigate.
Go to a trusted, certified mechanic
If stalling continues or you are unable to diagnose the issue with basic checks, visit a trusted, certified mechanic right away for further assistance. Ignoring the problem may lead to more complex issues that are harder and more costly to resolve.
For expert care without the hassle, you can rely on ACKO Drive service centres. Our trained technicians utilise advanced diagnostic tools to inspect every crucial component, identify the cause of the issue, and carry out repairs efficiently.
You can easily book your service slot online through the ACKO app or the ACKO Drive website, and we handle everything from doorstep pickup to a thorough inspection and repair/service with original parts.
How to prevent engine stalling
The best way to avoid stall problems and keep the engine operating reliably is through proactive care and attention to maintenance:
Perform regular maintenance
Regular maintenance of fuel pumps/filters, spark plugs, or ignition coils will help ensure the individual ignition and fuel components operate reliably when called upon. Properly maintained and functioning fuel and ignition systems reduce the chance of unexpected power loss and stalling.
Clean or replace air and fuel filters
If airflow and fuel supply are restricted due to dirty filters, the air and fuel will boil together in an unbalanced manner. For this reason, manufacturers recommend replacement intervals for a reason
Use the best fuel you can
Premium fuels contain additives that clean the engine's internal components, and even non-premium fuels have deposits that can restrict valves, leading to performance issues. In addition to sensors operating correctly, your engine is more likely to continue running smoothly
Check and replace spark plugs
Spark plugs can fail over time and need to be replaced according to the manufacturer’s recommendations. Clean spark plugs will ensure optimal ignition efficiency and reduce the likelihood of no-start situations or stalling
Keep sensors and the throttle body clean
Regular cleaning of the throttle body or MAF and O₂ (oxygen) sensors with a cleaner designed for engine deposits will remove build-up and will allow the sensors to read accurately without affecting engine performance, which can prevent stalling conditions
If dashboard lights or warning lights come on, get the vehicle in for a diagnosis immediately. The sooner you address the issue, the less likely it is to turn into a much larger and unmanageable level of repair and expense
Ensure idle speed calibration
Once service or parts have been replaced or repaired, be sure to confirm idle speed settings, which will ensure steady engine operation. Idle calibration will provide a smoother gear shift process and will help prevent unexpected shutdowns
Bottom line
If you continue to experience engine stalling, you are putting both your safety and your vehicle at risk. By thoroughly diagnosing the problem, acting on repairs immediately, and performing systematic checks on maintenance and component condition, you will be able to identify the source of the issues and restore your vehicle to its optimum operational performance.
Be mindful of symptoms, perform the proper checks, and always have dashboard warning lights diagnosed as soon as possible, so you can travel safely and with confidence.
Frequently Asked Questions
