Did you replace the HT leads and spark plugs?
You can also get CAT cleaner that try's to clear any s**te out of your car that may help my mechanic said to me when in doubt smash the cat out and buy another when your close to MOT time haha ignore that advice though
There is pre and post lambda - pre will effect running of the car if faulty, post will just bring up the light on the dash if faulty.