What OS / Tune file are you working on? I can't find either of those in COS-3 or the E38 tune I use......

I'v e been looking at dynamics a bit more and found another interesting point.

When running CL, if you get a large rich spike on throttle close, the O2's will pull a massive amount of fuel to bring the AFR's back to where they should be. If you then snap the throttle open again, you get a huge lean spike, as the O2's have pulled all the fuel out.

Reducing the impact factor / dynamic fueling and increasing "Wall Wetting Compensation" reduces the rich spike, which reduces the O2 correction and in turn reduces the lean spike on the next throttle opening.

I still think that the increase in richness in your example if just residual fuel in the intake at throttle close. You may be able to improve the fueling by altering settings to let the controller know that there is more fuel available to the cylinder at very low MAP settings. In the LS1, you would reduce the figures in B3401 and in the E38 you would increase the figures in B2014. In both cases just the 20kPa column would need adjusting.

I might try loading a bog stock tune in my car and see how the dynamics react, then try tuning them ( if needed :p ).

Simon.