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Ah – this is a position we’ve been in ourselves a few times now. It’s extremely unsettling to be just sitting there in your car, minding your own business, and perhaps waiting for the traffic light to go green when suddenly – phut – the engine stalls.
It’s not a good situation. In most cases, you’ll be able to restart the car and get moving again. If not, you won’t have any choice other than to safely push the car to the side and wait for help.
If your engine stalls while you’re driving at speed and the engine is operating far more quickly than just idling, this is likely to be a much more serious problem. You should get it checked out by a professional immediately. Get the car towed to an auto shop rather than driving it. When a car stalls, you lose all engine braking, and this represents a huge loss in stopping power. It’s a potentially fatal, highly dangerous problem to have.
What Does “Idling” Mean?
When an engine “idles” it means that it’s running at the lowest speed it can possibly go, yet maintaining efficiency.
When you start your car, the first thing the revs will do is go up, as the fuel injectors fire as much fuel as possible into the engine to get it going. After this starting phase, the revs will reduce down to a set amount. In most cars, this level will probably be between 600 rpm (revs/revolutions per minute) and 1,000 rpm.
An example of an idling engine would be when the car is parked, but the engine is still on. Another example is when you’re sat with your foot on the brake in a line of cars.
The technical dictionary definition of an idling car is when the engine is “disconnected from a load or out of gear.” In layman’s terms, it’s when your engine isn’t doing anything other than keeping itself running.
What Does “Stalling” Mean?
Technically, all “to stall” means is “to stop” or “to stop from running.” In the world of cars, it’s usually meant to refer to an instance when the engine stops at a time you don’t expect it to. When you turn your engine off in the normal way, this is also technically a “stall,” although it’s not usually referred to as one.
Stalling generally happens when the engine isn’t producing enough power for the task in hand. It’s a bit like the body’s response of passing out if you push yourself to exercise too hard. It can also happen when the power supply to the engine is reduced or affected in some way. Stalling is much more commonplace for anyone who drives a standard transmission. It’s something that always has a chance of happening, no matter how many years you’ve been driving.
In a standard transmission, stalling often happens when setting off or coming to a stop. If the clutch isn’t engaged smoothly enough or isn’t disengaged in time when coming to a stop, the engine will stall.
Why is My Engine Stalling When Idling?
There are several possible reasons for this to happen, some of which you should be able to do something about by yourself, without taking it to a garage.
The short version: there will either by a dramatic loss of power or a problem with where the power is going. Either way, the engine will be producing insufficient power.
The cause of your engine stalling will be something in one of these areas. We’ll explore a few of them for you in a moment.
How Does an Engine Produce Power?
Before going through the potential causes of your engine stalling, let’s have a quick refresher on how an engine actually works.
Fuel is stored in the fuel tank, which is generally located near the back of the car. From here, a fuel pump sends fuel through “lines” to your engine. At this point, it’s mixed with air pulled in through the air intake. Then it’s sent into the cylinder via a fuel injector (or carburetor on older cars).
When this mixture is inside the cylinder, a piston compresses it, before (in gasoline engines – not diesel) it’s ignited by a spark plug. In diesel engines, the compression alone is enough to self-ignite the air and fuel mixture.
This ignition causes the piston to be driven down forcibly in the cylinder. At the base of the engine block is the crankshaft. The crank rods, attached to the pistons, convert this reciprocal (up and down) energy into rotational energy. From this rotational energy, the wheels and drive belt parts are powered.
When the piston comes back up, the exhaust valves open, and the exhaust gases are forced out.
Many cars in the USA have either 4 or 6 cylinders, and some bigger ones have 8, 10, 12, or very occasionally, even more. All of the cylinders will fire at different times. When they have all fired, the engine will be in the same position as it was when it started. This is called one revolution, and it’s what your rev meter refers to when it measures “rpm” – revs per minute.
When your engine stalls, it’s generally because the rpm dips below the necessary level for that particular moment. When your engine is idling, there’s no strain on the engine, so it means there’s a problem with getting the power produced in the engine.
Potential Air Intake Causes
Without oxygen, the combustion cannot occur properly in the engine, and so it will stall. You may find something that’s preventing sufficient oxygen mixing with the fuel. This could be:
- A clogged-up air filter – you can check this by removing the air filter and visually inspecting it. If you aren’t sure where to find the air filter, consult your owner’s manual. If the filter is clogged-up, replace it with a new one.
- A cut or tear in the intake pipe or manifold – you may be able to fix this with some strong tape temporarily, but it’s worth replacing the part in the long run.
- A problem with the throttle body – this is what’s connected to your gas pedal. When you press the pedal, a plate opens, allowing more oxygen into the engine, creating more forcible explosions, and increasing the engine’s power output. This means you speed up. When you’re at rest, this plate should be ever-so-slightly open to allow a small amount of air to continue to power the engine. If it gets clogged up, this will prevent this from happening. You can remove it and clean it yourself with a cheap can of parts cleaner, available from your nearest parts store.
Potential Transmission Causes
The transmission is what drives the wheels. Potential problems that may cause stalling include:
- A malfunctioning torque converter or torque converter solenoid – if these get damaged, power can’t be received and transmitted as efficiently. Unfortunately, in this case, you will need an expensive transmission rebuild.
- Low transmission fluid levels – use the dipstick or onboard computer to check the levels of ATF. If there isn’t much in there, top it up. You should also check for leaks while you’re at it.
Potential Fuel Causes
An engine may stall if it’s not getting enough fuel to cause these combustion reactions. You should watch out for:
- A malfunctioning fuel pump – this can be tested by professionals using electrical testing equipment.
- A problem with one of the fuel lines – look for any visible cuts, tears, or other damage to them. If there’s a problem with one of these, we would advise, again, taking it to a professional mechanic.
- A problem with the fuel injectors – sometimes, these stop working properly, and it may be worth getting some new ones.
Other Potential Problems
As well as all the above, you should also check for:
- Whether or not your car has old spark plugs – you will likely feel a loss of power while driving if these are the problem. It shouldn’t be too difficult to replace spark plugs by yourself. You should also check the ignition coils at the same time.
- The condition of the oxygen (lambda) sensors and mass airflow (MAF) sensors – faulty readings from these could cause the car to stall. A mechanic with a code reader can tell you if there’s a problem with these.
- Whether or not the engine is holding pressure properly – get a compression test done from a professional garage. If there’s a problem here, it’s a big one.
We hope this article has been useful to you. We would especially recommend checking the throttle body, the air filter, the intake manifold, and the spark plugs, as these will be the easiest to diagnose and fix by yourself.