What model C172?

It is an old but nicely maintained 1974 C172 in our flying club, with
(Mph in ASI), but with no alternate air intake. When I encountered
this problem, I was thinking that I should fly our club's C182 or
ArrowIV in this soupy weather. Fortunately, I had my friend who is a
student pilot to take care of radio dial rolling. That helped a lot.

I am sure VSI did not have oblivious bounce because I tried to slow
down to attempt decreasing the oscillation. But it apparently did
not help too much; probably decreased the range from +-250 to +-150.

Thank you guys for provide valuable information. I will forward this
to our club's forum.

-cpu