98' Civic LX (auto) subtle idle issue. What am I missing?

SO I have a 1998 Civic w/ 142K thousand miles and for the life of me I can’t track down this idle issue. I’ve had the car for six months and its had the issue the whole time of my ownership.

SYMPTOMS: Idle surges up and down roughly 50-100RPM about once every second. With the surge the electronics/lights flicker up and down (very subtle, not a big shift). Also, with the surge there’s a really subtle noise, like a belt squeak.

ATTEMPTED FIXES:
– Cleaned IACV and retorqued gasket, no effect.
– Cleaned throttle body, no effect.
– Cleaned and retorqued ground cables, no effect.
– Cleaned battery terminals, no effect.
– Changed fuel filter, no effect.
– Changed and bled coolant, no effect.
– Timing belt and water pump service recent, no effect (idle surged before and after service!).
– Accessory belts changed recently, no effect.

OTHER NOTES
– The car also has an exhaust leak between the downpipe and the long pipe (I know exactly where it is, used the wrong exhaust gasket – haven’t gotten around to replacing yet). Not sure if this could be related, had the idle issue before I changed the downpipe.
– Catalytic converter recently changed.
– Air filter and oil recently changed, but again, issue existed prior to these changes.

If you have any ideas of what it could be, please let me know. I’m guessing the answer is replace the IACV, but I’d rather not throw parts at it unless there’s a clear diagnosis. Also, not sure if PCV could cause an idle issue this small? I could try replacing that as well, but I’ve been too lazy to pull it out (it’s buried under the fuel injectors and air box on the D16…).