If you disable auto-zoom, then you can Alt-drag with the Zoom tool to zoom vertically. Is this what you want?
See "Pan and zoom in the Graph Editor" for this and related instructions.
If that doesn't answer your question, answer back here and/or leave a LiveDocs comment.
I don't think there is any command for auto-zoom in the preferences.
when I turn off auto-zoom, I use spacebar+option to engage zoom tool.
Ah... So, spacebar+alt (option) and dragging with the mouse works... Even though it just shows the zoom tool with - sign, when you drag it will zoom in or out depending on your mouse movement...
Thanks for the help..
What we should really have is an ability to map keyboard shortcuts to any/every thing/function in the program. I'd kill (not literally) for the ability to map an individual keyboard key, without modifiers, to toggle the graph's autozoom feature. I'm constantly turning it (autozoom) on/off.