Yeah I currently don't have the A/C assembled. The condenser from Denso is backordered until mid-October. So I don't have any A/C parts to get in the mix. I did however noticed my A/C idle-up VSV is not testing in spec at all (open resistance between the two contacts). So while waiting for a new one, I capped off the two vacuum line connections at the A/C/P/S diaphragm on the intake just to see if there was some issue there but it made no change.

Updates:
- Installed new distributor/cap/rotor (non-OEM), set air gap to match OEM one to 0.30 mm. No change in behavior at all.
- Installed new Denso fuel pump. Previous one in there was a Denso unit. I was actually hoping it was a cheap one that may have been causing the issue. But I replaced it anyway, no change in behavior.
- Swapped in a used EFI solenoid I got off eBay. It didn't test in spec (like my current one). No behavior change.
- Did a prolonged series of tests pulling individual spark plug wires and watching the tach on the timing light. This is hard to audibly hear any differences, since running on 3 cylinders masks the slight misfire and shakes I would normally see. The only thing I noticed, was the range in idle variation was about 15 to 20 RPM's across all 4 test scenarios. When all 4 are plugged in and it's doing it's random shakes, I get a 30 - 50 RPM fluctuation. I think this was inconclusive from a test perspective as I couldn't hear or see anything that points to a particular cylinder.

New Theories:
- Fuel Pulsation Damper: This is the only part on the EFI fuel delivery side that I haven't replaced. Research shows these don't usually cause idle/running issues (that's reserved for the fuel pressure regulator), and if they fail, you basically just get a massive fuel leak. However, I noticed from pictures, mine was missing this plastic cap, but more importantly, was missing a set screw in the end of it. Apparently, the screw is set from the factory to control pulses from the fuel pump, and if anything, affects abrupt changes in fuel delivery (not idle). Strangely enough, if this screw is gone, it's supposed to leak. Mind doesn't leak, but I'm starting to think if it's not damped correctly, if the fuel delivery isn't metered properly it could be an issue. Regardless, the part is fouled up and I ordered a new OEM one to take this out of the equation. If the screw is gone, it allows the diaphragm to go in and out more than it should.
- Exhaust Leak: I have the LCE header and it's clamped between the header, o2 pipe, and catalytic converter. I noticed some black soot on a clamp before the o2 sensor, but I don't really hear any noticeable leaks. This could definitely cause a problem especially since it's pre-o2. But I tightened up the clamp, moved it around a bit in different positions, and it hasn't changed anything noticeable. I need to get a hanger re-welded so I will ask the shop to check for exhaust leaks, as I don't have a good way to test for minute leaks on my own.
- Fuel Injectors - Flow not matched or slightly leaking injector - Although these are new from LCE, and they are rebuilt OEM, I don't have any confidence from their product description as to how these are tested. I received no sheet indicating the flow or patterns across all 4. Also, I waited about 8 months after ordering these to installing them, and I've heard that's not a great idea and they should be installed within 30 days of being rebuilt. I found another company that provides OEM Denso injectors for a good price (MotorMan), and they also include test and flow sheets. Furthermore, they flow test and lubricate the set on order so they're not sitting around in a warehouse since who knows when. This would be my last ditch effort, but I may bite the bullet and order 4 of them.