no control over engine speed!

help. my clio 1.2 16v D4F 03. on the way to work the engine started to pack up. i pulled down a quite street. the engine speed was all over the place. when i help the pedal at 3000rpm the needle wound drop down to 1000/1500rpm and back up. some times cutting out. i did get home but half way it went in to save mode.

ive had a new lambda sensor. throttle body has been cleaned.

ive got a second hand on from a running engine.

can you just swap these over?

any ideas of proplem? if thre other body dont work im stuck