94 348 Spider A/C inlet box air filter crumbling - looking for part

That's not a filter, it's just a gasket that seals the inlet of the evaporator housing to the front deck lid. Are you certain that's what you're seeing coming out of the vents? Because in my experience the foam bits sprayed out of the air vents comes from foam sealing rings around the circumference of the flapper valves that shut off airflow from the individual vents (the flappers that are controlled by the rotary wheels on each vent).

The only solution I know of the that problem is to remove the vents and clean the remaining foam rubber off of the flapper valves. The valves will no longer be as effective at closing off airflow but at least you won't have sticky bits of foam rubber blowing all over the interior.

If anyone has any ideas for a replacement seal for those flappers I'd love to hear about it.

 

Maybe get some standard weather stripping or the larger AC foam vent strip and cut it to size. Maybe with a friction fit notch rather than adhesive. But fit it to the part constraints, regardless.

 

My main advice regarding removing and repairing the vents is that the plastic is fairly brittle and can break easily, especially in the areas that hold the moveable slats, so do your best to avoid putting any pressure whatsoever on the center portion of the left and right vent assemblies.

I suggest removing the instrument cluster and the trim pieces surrounding the left and right vents before attempting to remove the vents themselves. It's much easier to push the vents out from behind than it is to pry them out, and you can kinda sorta see the retaining tabs too, making them easier to manipulate. Take your time and avoid getting impatient because it'll take a lot more time to repair anything you break than it will to figure out how to remove them intact. At some point in the past the vents in my car were damaged in several ways and it took me lots and lots of time to get them back to fully functional.

If I can remember to do so I'll try to take and post a pic showing where the retaining tabs are on the outer vents since those are out of my car while I'm installing new speakers. The center vent is easier to deal with because it’s more robust. I have been able to just push it out from behind after the instrument cluster is out of the way.

If you find a practical and tidy way of replacing the foam please detail it here or in the 348 section. IIRC, the flappers were assembled around the foam and after everything that I'd been through with the vents themselves I decided to avoid messing with the flappers, choosing instead to just dig all the old foam out and clean everything up. But if there's a way to do a professional job of replacing the foam without undue risk to those NLA parts I'd like to know about it.

Best of luck and post pics of your project when it finally cools off enough to get into it. I'm a ways north of you but it has been even more humid than normal this summer, so I can only imagine how it is there. Although I will say this would be a great indoor project once you get the vents out, but it's tough to be patient and careful removing those pieces when you're sitting inside a leather lined sauna.