318 mystery problem, somewhat solved!

I'm not too familiar with the fast system, but I do believe that it has to do a bit of "learning" while driving for it to fully dial in for your specific engine. Based on map, tps, and o2 inputs. If it's falling on it's face after hard acceleration, if it doesn't adjust fuel supply quickly enough, you may be flooding it. Or, it could have something to do with your IAC. If for some reason you're IAC is closing fully under WOT, it will take it a second to readjust for idle.

Again, I don't know much about the fast system, but those are two things to consider perhaps.