What are the reasons for car acceleration problems?

The reason back to the drivers ...if one car has two drivers that will make many problems in the engin and in acceleration ....the second reason relted to the company making car...about efeincy of materials maked this point

weak fuel pump or Dirty fuel injectors 

•  1-Mass Air Flow Sensor.
• 2 – Oxygen Sensor Malfunction.
• 3 – Malfunction of TPS.
• 4 – Dirty or Clogged Fuel Filters.
• 5 – Clogged or Dirty Air Filters.
• 6 – Timing Belt.

Faulty acceleration pump or blocked nozzle in the venturi could be possible reasons, or the complete opposite like engine misfire due to overflooding. In Injection pump systems, it could be a number of things from air lock to improper injection nozzle flow to a faulty spring. Still the modern EFI systems are more efficient and reliable because of reliable air sensor,  throttle positioning sensor and the electronic management system .