I have bought a 2003 Peugeot 206 GLX 110 and it is has acquired what I take to be a flat spot (around 2000 revs) because it will not accelerate or decelerate smoothly. The anti pollution warning eventually appears followed by the engine diagnostic warning light which stays on permanently. I have returned it twice to the Peugeot dealer and they tell me that the problem is a faulty speed control sensor which they have replaced, but the problem persists. I am having doubts about this garage and wonder if this sensor has anything to do with the problem. Would the s/c sensor make a difference? What else might be wrong?