90 Civic won't smog. Full rich at idle.

Got a problem with my 90 civic 3 door 1.5 liter. Car failed as a
gross polluter at idle. I did a bit of troubleshooting and have found
that even when the car has warmed up it seems to think it hasn't and
is running so rich at idle the O2 sensor is pegged at .9v. If I rev
it up the loop closes and I can see the voltage jumping between .2 or
so to .9. Once it drops back to idle it continues to peg at .9v. I
had replaced the O2 sensor with an aftermarket one a year or so ago
and have just dropped the big wad on a new honda one which will be
installed tonight in hopes it will fix the issue. Last weekend I
replaced the thermostat just in case the coolant temp was the issue.
Trying to work my way up from cheapest to most expensive. Only other
thing I can think of is the computer (gulp). Anyway, if anyone out
there has a clue as to what it may be I'd love to hear it.

 

My 88 truck failed, but the attendant killed the test as "overheating"
rather than label me as a gross polluter. Make sure you get a pre-test
when you check your o2 fix, if it's not already too late.

I took the truck to the dealer. They said there was a problem with the
thermostat that kept the truck from warming up properly. I think they let
it idle until it got hot enough to pass the test. In my case, I was only
charged a normal "smog". I might have been able to fix it, or get it
fixed, but I din't want to get branded as a gross polluter, which stays
with you for a while in California, as if every test after that is
scrutinized for legitimacy.