87 E 150 fault codes # 12 & 41/ ref

6cyl. 300 4.9 o.h.v type:Y with a manual tranny 4spd overdrive. Went to get it smogged an failed .Mechanic told me it was either 02 sensor or egr valve checked egr and it opens and closes fine.Plus the egr is new.Idles perfect it has never idle this good before .Use to surge when idleing and sometimes die on fast stops.Hope this will help .Ialso have the VIR report but I can't read it. again hope this helps .NEED TO PASS SMOG