You could simply unplug and remove the accel pedal assembly from the car and then dry it out to see if that cures the issue but I'm not a gambling man so wouldn't advise just changing out the pedal just yet. I always like to proove a part is buggered before replacing it but that's just how I run my business... I'm not sure as i've never had to 'Clip' a Clio II RS yet but I believe you can't just plug in a new pedal and expect it to work. Of course, I could be wrong as we don't need to on the Peugeot 308 that use a similar setup however I'm certain I've read a tech note saying you need to 'Adapt' the new potentiometer ranges on a 'Clip' as we do with EGR Valves.
Personally, If it were me the first thing I'd do is get the car plugged in on a decent, local, diagnostic rig being run by someone that knows exactly what they're doing to see if the "ACTIVE" code becomes a "MEMORY" after the car's warmed and also to see what resistance values the two tracks are outputting.
Just a quick sub-question for you... what kit did you use to get the P0120? Some cheap code readers have been known to give phantom codes especially on the Clio II's
Mick