93 Civic low idle at operating temperature

I have a 1993 Civic LX 1.5L that I got for free because it needed a bunch of things done to it. It has 320k miles on it and I just thought it would be interesting to do some of the repairs that it needed on a car that wasn’t my daily driver.

When I got it, it had a high idle on startup and I adjusted the FICV as described in the videos. Once the car was warmed up though, it would idle really low, sometime like it was going to stall, but it never did. The water pump was leaking so I replaced the timing belt and and water pump as well as the oil pan seal, and crank and camshaft seals. At the same time I replaced the valve cover gasket and the spark plug tube o-rings since they were leaking. Since the car had an old aftermarket distributor cap, I just went ahead and put OEM distributor cap, wires and NGK plugs in the car.

So the good news is that all the oil leaks appear to be gone and the car seems to run fine except once I drive it 5-10 miles it still idles really low. It never stalls, but it stumbles like it wants to.

I followed the idle relearn procedure in the Honda manual and I can’t seem to get it to idle at the proscribed rpms with the IACV unplugged so that made me think that something was going on outside the IACV.

To try to diagnose the issue I have tried the following:
Re-bled the coolant
Check for vacuum leaks
ECU reset
Idle relearn
Checked the TPS voltage
Checked the timing
Checked the components of the distributor
Checked the fuel injectors
IACV opens when 12v applied

Replaced:
Oil pan seal (Fel-pro), Cam/crankshaft seals (Fel-pro), Valve cover gasket (Fel-pro), Tube o-rings (Honda)
Exhaust (except the catalytic converter)
Spark plugs (NGK), wires (Denso), distributor cap/rotor (Honda)
Timing belt (Gates), belt tensioner, water pump (Aisin)
Fuel filter

Based on Eric’s recommendations I see that he suggests maybe replacing the aftermarket PCV with an OEM. I could also, check the timing belt tension again, but I followed his video and it seemed like I had it tensioned correctly. I also considered the fuel pump, but wasn’t sure that would only be a problem when the car was warm.

I’m just looking for some ideas of next steps without dropping money on parts. I have the Honda manual and have gone through the flow charts for idle problems and it seems to point to the IACV or ECU (Flow charts end in “try a known good”), but I was hoping to have a better sense that this was the problem before buying those parts.