1990 Legacy AWD MT CEL not working? Plus weird relay issue?

[CharlieLS]

Hi again!

Tried searching the forum for similar issues and couldn't find exactly what I was looking for - this might be two issues, or fifty-three issues, or they might be related to one unifying issue, so I'm just gonna put it out there.

Recently (last 6 months or so), when I turn my ignition to "ON" without starting, the check engine light flashes (instead of just being steady-on) and there's a relay clicking constantly.  I think it's probably the fan relay, because the fans also come on, but only for a second, then it clicks off again, sort of like when the green diagnostic connectors are connected under the kick panel, except they're not.  Don't know if those two things are related (the CEL rapid flashing in "ON" position and the relay clicking), but the second part of the issue, or maybe a brand-new issue, started today.  While driving around today, after having installing a new battery a couple days ago, the check engine light came on steady.  So I stopped, attached the test connectors (the black ones) and got a fistful of codes.  But the weird thing is, while waiting for them to cycle through again so I could double-check them, they changed.  As in, started throwing codes that don't exist.  Like..."8." and "5."  It looks like the CEL got interrupted in the middle of flashing, so like, going from a long flash to a quick flash - maybe the code was supposed to be 18, but the long flash got cut off and made a short one, making it look like 8.  This happened a few times, to a few different codes, leaving me not knowing exactly what the hell numbers I'm looking at 😂

What I *think* the codes were trying to say:

45,23,24,13,14,15,16,18? (Atmospheric sensor; airflow sensor; air control valve; cam angle sensor; fuel injector #1-3; and oh wait there is no code 18 so I really have no idea). 

The car appears to be driving fine.  No stumbling, no cutting out, no weird smells (mostly).  The only eyebrow-raising thing as far as function goes is that when I first installed the new battery (fully charged, of course), it didn't want to start right away, and then stumbled, almost died, and blew a lot of smoke (light-colored) out the tailpipe (sort of like my previous MAF problems, which I thought were solved).  But once I got it to stabilize and the smoke cleared, it's been running fine since then, and only hesitated slightly to catch today after I pulled the codes.  

Does anyone know what the issue might be?  Bad ECU, maybe?  It's been replaced once, but not terribly recently, so I don't know how long the things should last.  Or am I overlooking something really basic?  Many thanks!