really high idle

Vacuum advance distributor? If so, is the hose connected to a timed port? Does it idle ok then idle high after revving the motor; or does it just idle high without goosing the throttle?

I'm thinking the advance in your initial timing raised your RPM's up enough to increase the vacuum open and kick in your vacuum advance. Or if the hose is connected to the manifold port, then the advance would probably kick in at idle, depending on your vacuum at idle. If you've had the hose disconnected or it doesn't have vacuum advance...disregard my feeble attempt to solving your problem.

I had a fun time playing with a vac pump connected to my distributor and seeing where the vac advance really kicks in. I ended up with it set to kick in at roughly 12 1/2 lbs of vac, car idles with around 11 1/2 lbs of vac.