There are several possible reason why your car’s engine dies when throttle is applied, including problems with the fuel system, ignition system, electrical system, and air intake system. Let’s go over each one in more detail to better understand why this can occur.
Fuel Pump
The fuel pump’s job is to literally pump fuel to the engine. If the pump fails entirely, your car will be unable to start. However, a warning sign of a malfunctioning fuel pump is hesitating or even stalling out when applying the throttle. This happens because the engine is starved of fuel and cannot complete the normal combustion cycle.
Fuel Filter
The fuel filter serves to filter out any contaminants from the fuel before it moves to the engine. It is important to note that the engine’s fuel injectors (which spray fuel from precise tips into the combustion chamber) are delicate and have very small openings, so even seemingly miniscule amounts of dirt can clog them and cause problems with your car.
So if the fuel filter is not working as it should and leads to contamination at the fuel injectors, the engine can die on throttle application, and in severe cases be unable to start at all!
Changing the fuel filter yourself is something most people can do if the have worked a bit on cars. A fuel filter will not last forever. Often It’s fine for the first few years when the car is new, but after some years its good to change it every 20,000 – 25,000 miles, or eveyer 1.5 – 2 years. Which ever happens first of those two.
Ignition Coils
The ignition coils provide electricity to the spark plugs, which in turn provide the spark that serves to ignite the air/fuel mixture in the combustion chamber. If these coils malfunction, the engine can die upon acceleration, if it even starts at all!
A common issue seen with one or more bad ignition coils (your engine has one coil per cylinder, so a 4 cylinder engine has 4 ignition coils and 4 spark plugs) is a misfire. This is when the combustion process is incomplete it one or more of the cylinders, and is very dangerous in that your engine will run rough (can die during throttle application along with being hard to start at all, etc.) and if not addressed can destroy your catalytic converters (a crucial portion of your exhaust system that filters out pollutants and are mandated by law to have installed and functioning on your vehicle to pass emissions inspections).
Although a misfire condition can be caused by things other than a bad ignition coil, this is always one of the suspected culprits and normally the misfire is accompanied by a check engine light on your dashboard, it might even be flashing (if it is flashing, you need to stop driving your vehicle as soon as possible to avoid potential serious, and expensive, damages).
Spark Plugs
As noted above, the spark plugs are what provides the spark needed in the combustion chamber. If one or more of these are faulty, either due to age, oil contamination, or another issue. they can create the same misfire issue that bad ignition coils can.
Without knowing the cause, both bad spark plugs and bad ignition coils can cause similar if not identical appearing problems, which includes dying on throttle application, hard starts, rough idle and overall rough running conditions, and in severe cases a no start condition.
Vacuum Leaks
Your car’s engine has to draw in air to function. If there is a leak somewhere in the air intake system, you might find your engine stalls when you try to accelerate. Like the other issues, this too can be accompanied by a check engine light and misfire condition, as well as hard starts and rough running overall.
A unique occurrence with a vacuum leak is that you might be able to hear a hissing noise coming from the engine bay. This is the sound of air escaping what should be a sealed system.
Idle Air Contol Valve
One part of the air intake system is the idle air control valve, which functions by working with the car’s ECU (electronic control unit) to ensure that the correct amount of air is let into the system. If it does not perform this job properly, your car can stall out on acceleration.
When you press the gas pedal, the throttle body is supposed to open and let in air. Too much or too little air will lead to problems with overall performance, which is why a valve is used to monitor the amount of air let in.
If this malfunctions, your car can stall and will often result in a check engine light on your dashboard.
Electrical System
Your car needs a battery to run, and the electrical system relies on a host of wires and connectors to transmit information and keep the car running.
If the battery terminal connections become loose or corroded, the car might simply die when you hit the throttle. This is because there is no longer a good connection sustained and while the car might intermittently turn on and run, it is also more likely to just stall out at seemingly random times.
Other connections, like the wires to the ignition coils, for example, can become damaged (perhaps by an oil spill or other contaminant, or even something like a rat burrowing into the engine and chewing wires) or worn out with age and need replacement.
Conclusion
If your engine dies when applying the throttle, it is clear there are multiple systems, and more than one component within those systems, that can be at fault. Furthermore, there is no reason that multiple systems are not in needs of repairs, complicating the issue further!
If you have a code reader (modern vehicles use OBD-II), this can often help reveal where the problem is. If you do not have a reader and/or do not want to purchase one, local auto parts stores as well as dealerships with service centers, and general automotive service centers, will have code readers and will often read the codes for free.
However, if, for example, a misfire on cylinder 3 is found, this does not tell you if it is a wiring issue, a bad ignition coil, or a bad spark plug, so further investigation is often needed to precisely find and repair the problem.