The throttle plate was sticking, and opened it up to find lots of black grime, which I cleaned out. Now it is working nicely, but it begs the question -- how did that stuff get there in the first place? Is it symptomatic of other problems that need to be fixed? There is a small black rubber hose going from the valve cover to the air intake, presumably to recirculate fumes from that space.
Is the problem related to the fact that the engine uses oil? TIA.