Accelerator Pedal
On older cars the accelerator pedal would have been connected to a cable that connects the pedal directly to the throttle body. Modern cars use a 'drive by wire' system that essentially transmits the pedal position as a digital signal to the ecu, the ecu then manages the throttle position. This allows for more safety systems to come into play as the ecu has ultimate control over the throttle rather than the driver.
Accelerator pedals can have problems mechanically and also with the sensor. There is added complexity for automatic cars as the pedal will also have a 'kick down' feature that tells the ecu to apply as much throttle as the engine can handle.
Accelerator pedal sticks down
The accelerator pedal sometimes stays down after pressing it down to accelerate. It seems to be stuck to the floor sometimes and releases back to the normal position very slowly.
Accelerator pedal moves around more than it should
The accelerator pedal seems to be loose when pressing it, it feels like it moves from side to side more than it did.
Car not accelerating normally
When pressing the accelerator down the car does not accelerate as it's supposed to, there is sometimes a lag or delay between pressing the pedal and the car accelerating. The acceleration is sometimes slower than it should be and the car can feel as if it's hitting a limit that stops it going faster.
Car acceleration or performance is not as strong as normal
When putting your foot on the accelerator the car does not respond with the same urgency of acceleration. It feels like there is a lag between putting your foot down and the car accelerating, when it does accelerate it feels like a much slower change in speed.
Automatic Gearbox sticking
When you put your foot on the accelerator, or take your foot off the pedal, the car doesn't change gear as you'd expect. It can seem as though the car is struggling to select the next gear.