Initial test
CO 0.ooo 2nd test 0.000
HC 6 2nd test 3
Lambda 1.138 2nd test 1,159
Badly split servo pipe replaced
CO 5.775 2nd test 5.916
HC 189 2nd test 214
lambda o.839 2ndtest o.834
natural idle 10.443

So far we have checked fuel pressure,evap, blanked off EGR after smoke test showed slight leak,cleaned and reset throttle body,checked air mass meter(1.25v on tick over 1.73 @ 3000rpm)fitted correct plugs,checked ignition timing and valve timing (for incorrect fitting and sheared woodruff keys)have also checked for blocked exhaust.Vacuum guage show steady 17 hg on tick over removed o2 sensor and still steady 17.Inducing a big air leak brings co and hc to tollerance levels as in first test.The o2 sensor perfoms well initially but on reaching 80 plus degrees becomes stuck on 1.25
The vehicle drives well with instant mpg on dash rising to mid 20s on a run and customer has no concerns about mpg
This has had me round the bend any ideas PLEASE