Fluctuating neg. to ground on ignition coil

Stephan D said
Not sure if it´s corrosion or just dirt, but the advance is working properly when checking with the timing gun, and it revs smooth and freely without any problems if I push the throttle, the slight "misfire" problems is only at idle.

Are you sure you are not hearing an exhaust leak.
Most miss fires get worse with load and more throttle.
Very very strange it miss fires only at idle.