Why does my car have difficulties in acceleration?

Friday January 12 2018


Hi Paul, I currently live in Juba, South Sudan. My car is losing acceleration. When I try to accelerate between 0-20 kilometre per hour, the car first hesitates and thereafter accelerates itself. However, on the highway it acts normal. What could be the problem? I have tried to change oil and brake pads. But the problem persists. Dominic

Hello Dominic, you need a mechanic to inspect the condition of the electronic throttle potentiometer, throttle position sensor and pedal position sensor.

When you accelerate a car, like your Toyota Premio, the throttle potentiometer opens a valve for intake of clean air into the engine.

This air intake is metered and regulated to balance with the fuel delivered with the help of the engine computor (ECM).
The throttle position sensor and pedal position sensors help the ECM to monitor acceleration and respond accordingly by regulating fuel delivery.

The potential failure points are a (dirty) sticking damaged throttle valve or damaged throttle position and pedal position sensors. These can be tested with a meter or a computer diagnostic tool.

Self-acceleration as you seem to suggest can be caused by a faulty accelerator pedal unit which may be damaged by corrosion or moisture. Occasionally wrong floor mats can obstruct the accelerator pedal and cause self-acceleration when you brake.

Other factors that can hinder acceleration can be a faulty fuel system. A bad fuel pump, dirty fuel injectors or restricted fuel filter can cause poor acceleration. It doesn’t harm to look at the work plugs and air filter too which will also reduce engine performance if not maintained.