I've been trying to get this unmolested '89 SOHC coupe back on the road after sitting for a couple of years and have not been able to locate this idle issue yet. Any help would be appreciated!

I have narrowed it down to the vacuum, intake, IAC or EGR systems after replacing the ignition and fuel systems entirely. I'll list my symptoms below and would appreciate any input on which place to start first from my list above.

The car starts very well, runs well and never tries to die out. There are no check engine lights (CEL works). When it gets up to temp, the idle starts surging above and below 1000rpm, but never below 600 or above 1500rpm. It enters a steady hunting idle state when warm where it just floats up and down in rhythm every second or so.
The second part of this problem is a sporadic popping sound from the exhaust, which is also visible as a small rock or knock in the engine. This occurs at idle, and while under constant load, every couple of seconds at an inconsistent rate.

Wondering if this IACV is the best place to start, or the EGR is more likely the primary culprit?
iacv-aac-cleaning-and-testing-tutorial-t251133.html
240sx-egr-tutorial-t427162.html

Anyone have a good Seafoam / Gummout tutorial? Cheers!