I have a Peug 307 envy 1.4 16v I am constanly have the engine management light coming on, and lately it has been loosing power.. Basically I had a service, they change a filter on the car since then, every time my car is half full of petrol, or driving below 30 mph in traffic, the light will come on with the dash comp reading antipollution fault. I read in the handbook that if this happens to drive the car as soon as possible over 35 mph with reves high.. and also read on another site that putting shell petrol in will cure the problem.This does happen but as soon as i get to just below half full it happens again and lately the car has been pulling and juddering, and losing power.. the light flashed and cat convert fault come on.. But the mot the emmisions were fine and the exhust doesnt make any noise.. It's driving me made and i know it needs sorting, as soon as i fill up the light goes out and car runs ok ..

What can it be, will it be expensive to fix.. Surely if the cat converter is at fault it wouldnt make my car sluggish and loose power . the exhust would make a noise surely..

Could it be a dodgy sensor or the fuel filter be clogged !! Please help