Has anyone used one and passed emissions testing? I think the OEM one
on my 91 Civic has finally bit the dust and is why my car is failing
emissions and has slightly reduced mileage lately. Autozone has the A/
M ones for $23.

This comes after quite a lot of diagnosis effort. Today I think I had
the proverbial breakthrough: The purge cut-off solenoid valve (in the
evaporative emissions control system) was stuck in atmosphere vent
mode, whereas once the rad fan has come on once, it is supposed to
send a vacuum signal to the charcoal canister's diaphragm. I found the
electric signal to the solenoid valve was constant at battery voltage,
which tells me the ECM is not varying its signal to the valve, which
implicates AFAIC the danged TW sensor. With J Beam's observations on
the TW sensor of a few months ago, and slightly reduced mileage of
late, and some other things (like the importance of doing emissions
testing in warmer weather on these old Hondas and how much control the
TW sensor has in open loop operation) it all seems to add up.