1) What is the highest percentage lambda correction can affect the fuelling? Is it the same in both directions and can this be changed dependant on customer request?

Its set around 33% But can be changed if you require, although i fail to see why you would want to?

2) What is happening in transient conditions? Is the transition from closed to open loop instant or smooth?

Its smooth, although i prefer lean to rich to be a little harsher than rich to lean so that curve is slightly more agressive.

3) Can the PID control parameters (Proportional, Integral, Derivative) be changed on customer request?

Yes, but again, why would you wish to do so?

4) How do the CO pot and closed loop co-exist? Which is active at idle?

The pot under closed loop control affects the gain at idle only. This serves largely to trim the ecu to the sensor in laymans terms.

Appologies if this isnt clear, just come in from a night at teh syndicate and i am rather hammered. lol