Idle drop by 500 rpm?

So if the damper and light are correct, I guess I'll close the Secondary blades. Oddly enough when it started when cold after I open them up and fired right up and idle at 600 and then 400 in Drive..reset the screws to 2.5 out. Seemed fine, but the timing was higher than when we set it last. All I did then was adjust the timing, then the stalling came into play...