S13 KA24DE "Hunting" for idle, still idles with idle speed screw shut

[drifter92]

Now that my car has an OEM airbox and filter on it, it will stay running on it's own but it still has some issues. It doesn't like to run at 20 BTDC, it runs best at 30BTDC and when I move it to 20 BTDC while it's running the idle speed drops alot and it begins trying to die, so I open the IACV screw and it doesn't help, even with the screw almost completely out the idle is still low and weak. Brake booster is not even hooked up, and the port is capped, and doing this made no difference in idle. Also my intake manifold and air tube hold 9psi of air without leaking at all.

What I know:

intake manifold and everything behind the MAF holds 9PSI with absolutely no leaks anywhere, tested yesterday.

fresh gasoline in it

good fuel pressure, 30-40psi makes no difference

Engine harness is good, tested 2 of them

MAF seems to be good, tested 2 of them

Timing chains are correct, cams are correctly timed, 248/232 "hot cam" swap
(I have done this many times with no issues, ever)

TPS resistance is good, 2-10ohms @ 0-90 degrees

ECU is good, tested 2 of them

IACV is good, tested 3 of them

Distributor is good, tested 3 of them

Ignition coil is good, tested 2 of them

Igniter chip works

Coolant temp sensor is good, ohm tested it, and tried 2 of them

O2 sensor is brand new bosch, unplugging it does not help.

Injectors are good, replaced all 4 injectors, O-rings are good

Brake booster vacuum hose is good and sealed, with a check valve

All 2 vacuum lines used on this engine are good

ISR EGR block off plate installed

Emissions & EGE removed

Code 55 on the ECU (no faults)

Throttle body is clean and gasket is new & sealed with a tiny amount of RTV

Intake manifold lower PCV ports are welded shut

IACV hose is new and sealed well

Air regulator valve hose is good, no cracks

Ignition timing is good, 20BTDC

Spark plug wires are brand new NGK

Spark plugs are new NGK BKE5E-11, replacing the spark plugs actually made it a little bit harder to start.

S14 longblock with all S13 parts on it. S14 upper intake manifold, S13 lower intake manifold.

[unicoder]

Are you setting idle speed correctly? You aren't supposed to just adjust the screw.

Unhook TPS Harness, crank car, adjust screw, turn car off, connect TPS

[drifter92]

I figured it out, I was lucky enough to come across 3 bad IACVs. I bought another one after hooking up a consult scanner and reading all the sensor voltages.

The problem was that the IACV was stuck open and causing an internal vacuum leak from behind the throttle body to the intake tube and since it was internal, it did not show up when you boost/vacuum leak test the intake system.

FIXED