High CO indicates a rich mixture. So the failed emissions and the increased fuel consumption are related. Now its just a matter of "why". It is possible that the Lambda sensor has failed and is falsely telling the ECU to add fuel. Poor grounds and poor connections can cause this. I seem to remember an in-line connector somewhere that was common for corroding, causing bad Lambda readings, but I don't remember where it is off hand.

 

Do you mean the connector around the throttle body area?

 

Yeah, you've got the procedure about right

 

Okei

Roto : Can you list up all the things I should Try befor buying a new Lamda?

That I would really appreciate !!