I think the lambda sensor in question is a EGO (at least for my project), ie not heated like a HEGO or UEGO. So I suppose you are right in saying that it'll have very little input in the feedback control loop.
Would you recommend MAP sensor manipulation?
A digram of how the Lambda sensor works;
If we presume the engine is reading 0.45V being the stoichiometric value. In order to make the engine run leaner, the ECU needs to be fooled into thinking it's running too rich a higher voltage; a 0.1V increase to 0.55V for example. I'm unsure of the...