It’s a nightmare when your car stalls while at the stoplight. What does it mean when it stalls while at idle? What can be done?
In this guide, I’ll review the possible reasons a car will die while idling and how much it will likely cost to fix it.
What Causes a Car Engine to Stall While Idling?
A car may stall when idling if either the oxygen or mass airflow sensor is failing. This can also be caused by a stuck-open EGR valve or fouled spark plugs. The idle air control valve, throttle body, fuel system, or even transmission are also possibilities.
Here is additional information on why your car may be stalling at idle.
#1. Defective Oxygen or Mass Airflow Sensor.
A car has a variety of sensors to ensure that the air-fuel mixture of the engine is correct.
These sensors all share information with the ECM (engine control module) to determine how to manage the engine to get it to function correctly.
The oxygen sensor is located in the exhaust manifold and measures how much air is being expelled out of the engine. The mass airflow sensor is located in the intake air duct to measure how much air is entering the engine combustion chamber.
The ECM uses the sensors data to either decrease or increase the amount of air entering the combustion chamber. When either the air or oxygen sensor fails to send correct information the ECM will decrease or increase the air supply incorrectly which will cause stalling while idling.
#2. Stuck Open EGR Valve.
The EGR (Exhaust Gas Recirculation) takes a bit of exhaust and sends it back into the combustion chamber.
This lowers the internal temperature because carbon dioxide doesn’t burn as easily as oxygen, reducing the internal temperature of the engine combustion.
If the EGR valve sticks open, the exhaust gas continues to flow and messes up the air-fuel ratio.
This could also lead to being overly rich in the system. Your engine is going to stall without the right amount of power.
#3. Fouled Spark Plugs.
Spark plugs ignite the air-fuel mixture in the combustion chamber and as they age, carbon deposits form on the tip of the plug, making it harder to start the ignition.
This defect causes less power in the engine and would create a stall effect while idling the engine. Changing the spark plugs is a regular maintenance interval and part of the regular tune-up.
Copper plugs may last up to 30,000 miles but there are iridium or platinum plugs that will run for 100,000 miles.
#4. Throttle Body.
If your car is from before the mid-2000s, you’re likely working with a mechanical throttle body. When dirty or contaminated, it can impede airflow which can leave you with a stalling engine.
Cars built after this date will generally have an electronic throttle body. A defective throttle body can stall a car if something is wrong at the circuitry or connection point.
It could be a dirty throttle body however.
#5. Malfunctioning Idle Air Control Valve.
The idle air control valve or actuator maintains the RPMs in the appropriate range, especially when idling, by utilizing information from the ECM to establish what the proper RPMs should be.
If the actuator or valve is faulty, the engine could stall because the speed became too low. If a vehicle has an electric throttle body, then the vehicle most likely integrates the idle air control valve with the throttle body.
#6. Fuel System Issues.
We have talked about the appropriate amount of air in the combustion chamber but just as important is the right amount of fuel getting to the engine, because low fuel supply to the engine will cause the car to stall.
There are multiple different components in the fuel system that can be the culprit to low fuel supply. You could have a defective fuel pump, clogged fuel filter, etc. Symptoms due to fuel system problems can also present other symptoms that may be noticeable before you get to the point of low fuel supply to the engine.
You may also hear whinning noises, feel sputtering, notice surging, and have trouble starting the car. As the condition of the car gets worse, the engine will also run less efficient and you could find yourself spending more and more time at the gas pump.
#7. Transmission Trouble.
No one wants to hear that the transmission is where the problem lies because that sounds expensive, but it is a fact that the transmission could cause the idling issue.
The potential problem here originates in the torque converter because it connects the motor to the drivetrain in automatic transmissions like a clutch in a manual transmission.
The torque converter transmits power from the motor to the drivetrain, when it becomes defective or simply wears out, the torque converter locks up, and you get the resistance causing the motor to stall.
It could also be a solenoid as well, which is the electromagnet part that gauges and regulates the fluid pressure.
Diagnosing an Idling Engine
If you’d like to identify the issue on your own, follow these straightforward steps.
- Scan for diagnostic trouble codes. Use an OBDII code scanner to see if any faults have been saved to see which faults have occurred and repair the issue causing the trouble codes.
- Spray some starting fluid on the throttle body. If the engine runs normally during this period, the issue you are experiencing is in the fuel system.
- Check the fuel pressure. Mount a fuel pressure gauge on the pressure side of the fuel delivery system. A pressure reading of 40 to 50 PSI on a gas engine and diesel engines typically have higher pressure, but you can look at your service manual for a specific reading for your vehicle.
- Check for spark. Insert an inline spark tester between a good ground and the plug boot. Crank the engine. If you see a spark, the engine is getting spark. If not, your spark plugs need to be checked.
- Clean your throttle body, and if you have the capability, do a calibration with your OBD2 scanner. If you don’t have the ability, you may need to go to the dealership to have the throttle body calibrated.
If you are unable to gather any information with the steps listed, you may need a professional shop to take a look.
Cost to Fix Stalling Engine
The cost to repair a stalling engine is dependent upon what is being repaired. If you are required to put in a new oxygen sensor, you might spend $150-$500 in part and labor. If you needed to put in a new mass airflow sensor, you could expect it to run around $200-$350 total.
If you are required to replace the EGR valve, it could run about $250-400. You could clean the EGR valve for about $150-$200, however, it may or may not fix the issue depending upon the circumstances; and the EGR valve will need to be replaced anyway, sometime.
The cost to replace the spark plugs will depend on which type you put in. You would spend about $50-$250 for a complete tune-up.
Because a tune up is also dependent upon the parts you put in, and if you put in iridium or platinum spark plugs, it will be possible to go long intervals between tune up and you could go for about 100,000 miles.
You can possibly clean the throttle body to fix the issue. If that’s the issue, it will be easy because you just have to spray cleaner on it. If there is a circuitry issue, then maybe you have to buy a new throttle body, which will run $200-$650.
Except for those, with fuel system issues, you may have to replace a fuel pump, which runs $200-1000, and fuel filters which may run you a meager $50-$200.
These can all be some of the more expensive problems, transmitting issues. To replace a torque converter, if that is needed, input about $600-$1000.
However, it could have been the solenoid, which could be $15-$100, for which even if that is actually the problem, you could perform the repair yourself no need to pay a mechanic to charge for the labor for replacing the solenoids when you could do it at home yourself easier, if that is actually the problem.