Thermo sw controls egr, along with other controls for same.

Egr helps keep NOx low (you missed one hell of a band when you missed the Oxides of Nitrogen. Explosive sound.).

High co and passing HC indicates lean running (vac leak, maybe from missing lines), and lean out will make NOx high, too, as NOx comes from high combustion temps which are caused by too lean a mixture.

Not responsible for advice not taken...