Mercedes-Benz S420 Car shuts off when stepping on gas pedal Inspection at your home or office.

Common reasons for this to happen:

Let’s have a look at some of the more common causes that would make your car stall or stumble when you attempt to accelerate.

• Faulty ignition components: The ignition coil pulls power from the battery and delivers it to the spark plugs, which ignites the fuel and makes the engine run. The car will display a number of symptoms as the ignition system wears.

Misfiring is one of the first symptoms you will see as a symptom of incomplete combustion due to improperly firing ignition components. As the situation progresses you will have trouble starting the vehicle and your fuel economy will drop dramatically. A flashing “Check Engine” light may be associated with this issue.

Finally, as the ignition system reaches the end of its life, your car will misfire and start to stall. Expect the engine to sputter, cough, and jerk, especially at higher speeds. Irregular sparking will cause the car to stall and it may shut off completely when you bring the car to a stop.

• Faulty fuel pump: The fuel pump moves fuel from the gas tank to the engine. If the fuel pump is malfunctioning, the engine will be getting less fuel than necessary, which will lead to performance issues, and ultimately cause the vehicle not to start.

One of the first signs of a failing fuel pump is hesitation under acceleration. As the problem progresses, the car will lose power when idling, and eventually it may shut down completely.

• Bad fuel filter: A fuel filter strains the fuel before it reaches the engine, which protects the fuel injectors. They are essential to a well running engine and require regular replacement. If the fuel filter is not replaced at the recommended intervals, the performance and fuel economy of the engine may suffer dramatically.

A failing fuel filter may exhibit similar symptoms to a failing fuel pump. Power loss, especially on acceleration, may be the first sign. As flow continues to be impeded, the fuel filter may ultimately lead to a no-start condition, as fuel can no longer get to the engine.

• Vacuum leaks: The engine of a car is basically a large air pump. Air is drawn into the cylinders and mixes with fuel that is compressed and ignited. The air is drawn in through a butterfly valve, which creates a vacuum. The vacuum is used to power a number of auxiliary devices.

The tiniest of leaks can cause engine performance problems. Expect a rough or too-fast idle speed. Misfiring or hesitation during acceleration is another common issue with vacuum leaks. As the leak gets worse, the car will begin to stall. A hissing sound and an illuminated “Check Engine” light will typically also be observed.

• Bad electrical connections: Modern cars have an extensive electrical system, and a bad connection (or bad ground) can cause a number of issues. Dim or flickering lights can be a sign, as well as difficulty starting the car. The car will make a clicking noise, much like a dead battery or loose battery cable.

• Dirty or defective idle control valve: The idle control valve controls the amount of air that goes into the engine, which allows the computer to maintain the proper engine speed.

When an idle control valve becomes contaminated or stuck, it may lead to an unsteady and rough idle. The car will stall if the valve is too clogged or when it finally fails. If, while holding the accelerator pedal down, a small amount of pressure keeps the car running at a stop, the idle control valve may require attention. In most late model cars, this problem will usually trigger the Check Engine light.