True, but only enough to match the increased pressure - so an increased idle speed, but not rich running.

Of course, that is just based on conjecture on my part based on my understanding of how D-jet works. Perhaps the specially tuned idle mode (triggered by the closed throttle) is somehow fooled more easily by vacuum leaks? Or perhaps leaks down at the end of the intake runners create some sort of dynamic condition? I should mess around with my wideband O2 sensor and my 1800E sometime and see what I find out. You could simulate a badly leaking manifold gasket pretty easily just by loosening the collar on an injector and pulling it slightly out. Or unhooking the vacuum hose to the brake booster. And watch what the mixture does when that happens.