'96 Toyota Tacoma P0171 Lean Code

Well I'll be dipped... anyway 02's work the same. The B1S1 is looking better at 2500 but not at idle. Post cat 02 should not be oscillating. That indicates a lean engine condition as the cat is holding excessive oxygen. Should be a touch on the rich side 500-700mv at idle.

That vsv hose off should have given you problems. That's a source of a vacuum leak. Is the vsv working correctly? It's a vacuum switching valve which allows and stops the flow of vacuum. Believe it's tied into the evap system allowing fuel fumes back into intake. It should not just fall off.

scannerjohn - I suspect the VSV hose never got reconnected when I replaced VC gaskets a couple years ago.
Looks like I fixed it today! I went ahead and built a DIY smoke machine. I had a substantial leak out the bottom of the throttle body gasket. I had it off a month or so ago to replace the rubber coated plug on the back of the right valve cover. (oil leak). At that time I reused the throttle body gasket. I guess the manual means it when it says don't reuse .
I should have remembered rule number 1: Always check the last thing you fixed.
Anyway, a new gasket and my total fuel trims bounce around from -1 to +5. Huge improvement from 40%. Looks like I may have some small leaks around the EGR system. I'll save those for another day.
I still need to take a look at how the O2s are responding and verify the heater circuit integrity.
Thanks for the help everyone!