206 gti rough idle when cold

[chrisga]

Does anyone else experience this? If its cold my car seems to idle very roughly until it is warm when it is fine. Also if it is cold and seemingly wet weather i always get a catlytic converter fault appear ont he dash, which then downgrades to anti pollution fault after a while and then goes completely. If it is frosty but dry this doesnt happen.

Have i got a dodgy sensor somewhere or is it worse than that?

Any help/previous experience appreciated.

Thanks in advance.