Rough idle, 3.2 engine still runs with snorkel blocked

[TargaRich]

Long time lurker, pulling my hair out with rough cold idle issue. Runs at about 700 rpm for a few minutes and stumbles.
1985 3.2 Carrera, and I have checked the usual vacuum leak areas with starter fluid, propane gas, the works. All vacuum lines seem properly connected. Retorqued intake manifold nuts. Idle drops a little when I remove oil cap.
Engine runs rock solid at 800rpm after a few minutes, never a problem when warm.

Today when experimenting I sealed off the air intake snorkel completely, and the engine kept running fine with no drop in idle. I know the ICV valve will compensate, but where is the engine getting air from if the intake is sealed? Maybe a leak around air filter, but if that's not it, any ideas?

[Jack Stands]

Obviously getting air from somewhere. I know the rear clip on the air cleaner is a pain to get to and it may not be attached properly, allowing air to get by the air filter. Or perhaps a crack in an intake runner connection? Sounds like you've checked the usual suspects, but please share what you find with the group.