xsara 1.4 Petrol 04 plate?

Hi, just had a manifold fitted to the car and when I start it, it now shows the engine management light.
I have replaced one Lambda sensor on advice and it has made no difference, I have also swapped over the lambdas and it has made no difference the light is still on.
Quite interested in unhooking the control unit to clean it as advised for a picasso, is it the same procedure for a xsara or am I on the wrong path completely,
many thanks