2005 Citroen Xsara Picasso accelerating on its own when the car is wamed up

First check for codes,air leaks could cause symptom,then fuel system,you could do a return spill check to see that each injector is functioning correctly, and also pump advance ment device.

I remember reading somewhere that the accelerator cable is routed in the passenger footwell. Passenger's feet might be relevant. (couldn't get it to make a difference on mine).

Long shot really
Paul