[senormechanico]

I'm hoping someone can help more than the Chilton's manual has.

1995 Geo Metro 1.0L / 5speed with 160k miles.
Starts and runs great whether hot or cold.
Used mostly used on rural roads 35-50 mph.
Compression is 180 on all cylinders.
No oil consumption.
Exhaust pipe is black with a little soot ring around the outside as well.
I get about 42-45 mpg.
Ignition timing/valve timing are ok.

Everything I've tried has not helped with leaning out the mixture.

O2 sensor replaced no change.

I stuck my ocilloscope on the O2 lead when engine was idling(warm)
The O2 voltage changes, but the waveform is a whole lot slower than the book calls for, although it's inside the parameters. When I injected a little unlit propane from my torch into the air cleaner horn, the voltage went all the way to the end of the parameter. When I turned off the torch valve, the voltage and waveform returned to previous.

Any suggestions would be greatly appreciated.