Also, the standard lambda sensors are narrow band so basically only have a very limited range. Think of it as three signals; in the middle is near stochiometric, above is leaner than stochiometric and below is richer than stochiometric. They cannot indicate how far away they are from best mixture nor be used to really control the mixture under different load conditions. If stochiometric is not the desired mixture then narrow band sensors really don't do a whole lot of good.
