Bosch have done the hard work on this one.
A lamdba sensor that measures air fuel ratio that is extremely tolerant, accurate and the genuine article !
The 4.9 can cope with fuels other than normal petrol, even 2 stroke mix.
Genuine Bosch sold here, beware there are counterfeits round ! Use
.http://www.protect.bosch.com to check them out
5 Wire Wideband Oxygen Sensor
Bosch OE # 0 258 017 025 ( 0258017025 )
Motec # 57006