Variable Idle - 2001 V70

WE've got a 2001 V70 2.4, just a bit over 90k miles. The idle sometimes
wanders a bit...it will sit at 800 for a couple seconds, then rise to
about 1000 for a few, then drop back - up and down like that. Doesn't
seem to do it all the time, and mostly it's a minor annoyance.

Dealer suggested some sort of "intake blast" cleaning - $165. I used to
be in the dealer service business, no naturally I think that's a crock.
But I could be wrong.

Any other suggestions? Would a can of Sea Foam or Berryman B12 do any harm?

TIA...