hi !!
i have been n in Mauritania last month . I can assure you that Unleaded ( I mean "green" unleaded , ie fuel with 95 RON without lead , Its not availiable other than maybe in Nouatchott and probbably neither.
Definitely unavailable in Naouadibou . You will probbably struggle to get Super (Leaded 98) ´cos the only thing available is "Essence" (Leaded 92 RON)

All other countries (as of June 2006) they dont´sell unleaded at all . At least both Guineas , Sierra , Mali , Niger , (most of ) Senegal and most of Gambia . I simply can´t believe this "west Africa going unleaded" at all. -its simply not happening .

If at all , Id say that Africa is going diesel , and that most petrol stations are no longer selling petrol . Petrol is now only used for mopeds , and generators , and mostly only sold in Conveniences Stores (in Yellow plastic drums ) .Most Mauritanian petrol stations , simply only stock and sell diesel..

Havin said that , that Lambda sensor has nothing to do with the leaded / unleaded thing .It measures the oxygen avaliable in a gas (hence how rich/poor the fuel/air ratio is ) because catalithic converters are destroyed by alcanes (i.e. any free simply hidrocarbon , such as unburnt fuel -heptane/octane). so , in order to keep the cat converter safe , they need to minimize the amount of unburnt fuel , hence monitoring the oxygen . As long as there is oxygen , there is not probbably unburnt fuel , and the EFI can just put a little more fuel on it.

but leaded fuel has nothing to do with this. It will fu$%%ckup the converter , but definitely not the lambda sensor at all.

If you can live with screwing up your cat-converter , then your car is gonna drive , better , longer , and probbably faster using leaded fuel . I wouldnt worry at all about that

Have a nice day
Javier