vacuum leak at the shaft. Vac leak gets partially cut off when the arm torques the shaft in the sloppy bushing bore. Tick is probably the butterfly fluttering on the shaft on the stretching and about to fail butterfly plate screws.

The low power is a leaned out cylinder at the shaft vac leak. As the rpms rise and the leak becomes less as a proportion of total air flow, the mixture becomes ignitable and power comes back up to proper levels. You often get a vac leak misfire at idle that disappears as the rpms rise for the above reason.

Not responsible for advice not taken...