Any recommendations on what to do, what not to do to loosen up my idle
air control valve? What to use for solvent/penetrant that won't damage
it? Brake cleaner, gas, diesel, motor oil?

Back story is that van sat for 2 years due to bad ECU. Ran perfectly
before ECU died. 2.1 in an '87 Syncro

Now it idles at a pretty consistent 2200. Same thing on three different
ECU's I've tried. IACV buzzes (as I understand it should) when the key
is on, engine not running. Yesterday, out of idle curiosity (no pun
intended), I lifted the IACV and stuck my finger in the hole to seal the
vacuum leak I'd created. Motor immediately went to 900rpm which is where
it idles before ECU problem and two years of sitting. So, I WD40'd the
IACV let it buzz for a while, then put things back together. Now, each
time I take my foot off the accelerator, it idles steady, sometimes
right at 900, but often at another speed. Now, it's always less than 2200.

This suggest to me that the IACV was stuck, now is moving but sticky and
inconsistently. But I really have no idea what the thing does nor how it
works (or doesn't).

Am I on a useful path? Or, am I barking up the wrong tree? Suggestions?

Thanks

Raymond