Prius poor starting high fuel consumption

It's possible a faulty accelerator pedal module is to blame. That module directly influences the throttle valve position. Think of it like a dimmer switch for your engine – if the switch is faulty, the light (engine) won't behave predictably. Have you checked for any error codes related to the throttle position sensor or accelerator pedal position sensor? Also, does the engine idle seem unusually high or rough?

I have not yet checked for specific error codes related to those sensors, but the engine idle does seem somewhat rougher than usual. Could a diagnostic tool pinpoint a defective accelerator pedal module, or are there other potential causes I should consider before assuming the module is the sole problem? Could it be as simple as a dirty car throttle?

A diagnostic tool should be able to read the signals from the accelerator pedal module and see if they are erratic or out of range. While a dirty throttle body can cause similar idle issues, the poor starting and high fuel consumption lean towards a problem with the signal the engine is receiving from your foot. To be certain of the car throttle, I would recommend a visit to a workshop.

Following your recommendation, I took the Prius to a trusted workshop, and indeed, the accelerator pedal module was found to be defective. The repair, including the new module and labor, cost 205€. The symptoms have now disappeared. Thank you for pointing me in the right direction!