The most common cause of a stuck accelerator is floor mat interference, where the gas pedal gets physically trapped by a loose or improperly fitted floor mat. The second most common cause is a mechanical issue with the pedal itself, where internal friction causes it to stick rather than spring back when you lift your foot. A joint investigation by NHTSA and NASA confirmed these two mechanical defects as the only verified causes of dangerous unintended acceleration, with no electronic faults found capable of producing the wide-open throttle needed for a runaway vehicle.
Floor Mat Entrapment
Of all the causes, floor mat entrapment is the one most likely to produce a truly dangerous situation: high-speed, sustained acceleration that lasts for seconds or even minutes. It happens when a driver presses the gas pedal far enough toward the floor that the mat catches and holds it at full throttle. The U.S. Department of Transportation has stated that for high-speed unintended acceleration events lasting many seconds or longer, floor mat entrapment is the only cause NHTSA has been able to confirm.
This doesn’t happen with properly secured mats. It occurs when the mat isn’t anchored to the retaining hooks on the floor, when one mat is stacked on top of another, or when a mat from a different vehicle model is used. In the well-known 2009 crash near San Diego that killed four people, the floor mat in the Lexus ES350 was designed for a larger Lexus RX SUV and was much longer than the correct mat for that car. Toyota ultimately recalled nearly eight million vehicles in the United States over this issue and a related sticking pedal defect.
A Sticking Pedal Mechanism
The second major cause is a mechanical defect inside the accelerator pedal assembly itself. In this scenario, friction within the pedal mechanism increases over time, especially in humid conditions or temperature changes, causing the pedal to resist returning to idle when you release it. Unlike floor mat entrapment, a sticking pedal typically causes a slower, partial increase in engine speed rather than full-throttle acceleration, but it can still be dangerous if the driver doesn’t recognize what’s happening.
Carbon Buildup in the Throttle Body
In older or high-mileage vehicles, the throttle body (the valve that controls how much air enters the engine) can accumulate carbon deposits, dirt, and oil residue along its inner walls. This buildup forms along the “seat line” where the butterfly valve closes, making the valve stick or move sluggishly. The result can feel like a pedal that hangs or doesn’t respond smoothly.
A common maintenance guideline is to inspect and clean the throttle body every 75,000 miles, though smaller vehicles and hybrids can often wait until 100,000 miles. A practical rule of thumb: check it every time you change your air filter. If the throttle opening looks black, sooty, or coated with gummy deposits, it needs cleaning.
Worn or Frayed Throttle Cables
Vehicles with traditional cable-operated throttle systems (mostly pre-2005 models) use a physical cable running from the gas pedal to the throttle body. Over time, the cable’s inner wire can fray, kink, or corrode inside its housing. This creates friction that prevents the cable from sliding freely, causing the pedal to feel sticky or slow to return. If the cable is badly damaged, the pedal may not come back at all when you release it.
Electronic Throttle Sensor Failures
Most modern vehicles use electronic throttle control (“drive-by-wire”), where pressing the gas pedal sends an electrical signal to the engine computer, which then opens the throttle electronically. When the accelerator pedal position sensor fails, the symptoms are usually the opposite of a stuck accelerator: the engine may not respond to the pedal at all, idle speed may fluctuate, or the vehicle may drop into a reduced-power “limp mode” and trigger the check engine light. Despite widespread concern during the Toyota recalls, NASA engineers found no electronic flaws capable of producing the wide-open throttle openings needed for dangerous unintended acceleration.
Pedal Misapplication
One factor worth understanding is that many reported cases of “stuck accelerators” turn out to be pedal misapplication, where the driver is unknowingly pressing the gas pedal instead of the brake. A study analyzing accident data found 3,740 accidents clearly caused by pedal misapplication compared to only 39 that fit the NHTSA definition of true unintended acceleration. In none of those 39 cases did the driver attribute the event to their own error. This doesn’t mean it’s “the driver’s fault” in a blaming sense. It means the brain can genuinely misperceive which pedal the foot is on, especially during low-speed maneuvers like shifting from Park into Drive or Reverse. NHTSA continues to research whether better pedal placement and design could reduce these incidents.
What to Do If Your Accelerator Sticks
If your gas pedal sticks while driving, the priority is getting the engine out of the equation without losing control of the vehicle. The recommended sequence, based on emergency dispatch protocols:
- Shift into neutral. This disconnects the engine from the wheels immediately. The engine may rev loudly, but the car will stop accelerating. For a manual transmission, push in the clutch first. If the automatic shifter won’t move, press the brake firmly and try again (you may need to press the button on the side of the shift handle).
- Apply the brakes with firm, steady pressure. Do not pump the brake pedal. Hold constant pressure and let the car slow gradually.
- Steer to the side of the road. Once you’re slowing, guide the car to a safe spot off the roadway.
- Turn off the engine carefully. With a key ignition, turn the key back one click to the ACC position so the engine stops but the steering wheel doesn’t lock. With a push-button start, press and hold the button firmly for at least 3 seconds. Do not just tap it.
Brake Override Systems
Many vehicles built after 2010 include a brake override system that automatically cuts engine power when both the brake and accelerator are pressed at the same time. The system continuously monitors both pedals and, at speeds above about 10 mph, reduces throttle if it detects a conflict. Once engaged, the override stays active as long as you keep your foot on the brake. This means that in most newer cars, pressing the brake firmly is enough to regain control even if the gas pedal is stuck. Not all vehicles have this feature, though, so knowing the shift-to-neutral procedure remains important regardless of what you drive.