Yes the ECT is the blue sensor, this has a major influence on mixture.
It is at rear of head on inlet side, a bit awkward to get to but defo worth changing, if more than about 3 years old.
I am not sure what the std CO is on a std car, think ford did quote 1.5%, but they were a lot better/happier richer than this, most around 2% - 2.5%, so just tweak up a bit, you'll find it goes btter too.
Matt Lewis 01548 484488 sells the sensors, I would change the air temp as well if original or old.
tabetha