Spluttering/Juddering/Misfire

[Craigc2]

Hey Slight problem with my Citroen c2 A couple of weeks ago my car decided to go abit strange. It was Misfiring and Juddering quite badly it got to a point i was putting my foot down in 1st and the revs wouldn't go above 2k Revs.... Idle was quite Lumpy also and was struggling not to stall. I got it home left it a couple of days and all is well again. I decided to change the downstream o2 Sensor. That is Running ok now But its still not right..

Should i also change the 1st Sensor which monitors the Clean air? As i have a de-cat manifold and i have the 1st lambda Sensor Sleeved up in a Lambda sensor sleeve.

All the diagnostics machines have it down as the 1st Lambda that is faulty.. But surely if the 1st lambda isn't correct that may be giving the 2nd lambda a False reading?

Im in desperate need of getting this sorted... Can anyone help?

Cheers