I think it maybe can be different from country to country.
- Overhere in Holland its 4.5% till 1991.
- From 1991-on its 3.5%.
- But cars fitted with cat and lambda control only may have 0.5%.
- And then from 1994-on there came newer regulations for petrol engines which says to meet certain Euro emission standards with a 4-gas test. 0,5% at idle and 0,3% max. at 3000rpm, lambda between 0,97-1,03.