1996 Gravel Express EJ20G idle problems

[MCSRHelix]

I have a customer's 1996 Gravel Express in the shop atm. On cold starts it will run then die 5 times before barely idling a hair above the minimum line. It seems to be idling on 3 cylinders unless the MAF is disconnected. (MAF is reading 1.2 volts at idle if i depin the just the sensor output and probe the pin on the sensor with the rest plugged in so it still "operates")

This customer also has another GXE so I have been able to swap parts that are known good. So far I have tried swapping the MAF and ECU and neither have failed.

The vehicle is setting Codes for the MAF (23) and IACV (24). If I disconnect the MAF the vehicle runs perfectly, so I have ruled out any mechanical issues (Injectors, valve lash, etc..)

I have done extensive electrical testing to rule out any wiring related to either circuit or ANY sensor circuit to be faulty.

I replaced the Main Relay under the right-side kick panel with a known good one. Battery Voltage is 14 volts when running. There is no voltage drop on B- to chassis or engine grounds. No voltage drop on B+ while running or key ON.

I have replaced the O2 sensor with a brand new NTK sensor with the correct plug.
I've also smoke tested the entire induction system and even pressure tested the intercooler.

The Throttle Position Sensor is sitting at 4.75v while closed and .9v at WOT (Yes, the idle switch works too (0v at idle and 4.5v beyond that) ). I've scoped the cam and crank sensor to verify signal integrity (both at the sensor and at the ecu)

I cleaned the IACV for shiggles and it had no change. I can see it operating if removed and have verified it can sweep from end to end with no snags.

The plugs were changed at the beginning of the diagnosis and the coils are relatively new (stock, no torn or cracked boots)

The coolant temp sensor seems to work and does change fueling as it warms up (gets slightly better at operating temp)

I put a wideband in the O2 sensor hole and discovered it is running lean (20:1) after it enters closed loop (runs fine for 4 seconds after startup in open loop)

If anybody has any Ideas as to what this could possibly be please Lmk, I am out of ideas.

Thanks

[jdmvip]

Welcome, it's nice to still hear about users with EJ20G. I am still leaning towards it being the IACV and/or MAF, these are somewhat common issues that I personally experienced. You observed the IACV working fine but what if it's an intermittent fault?

[jdmvip]

One other possibility could be fuel related too, did you check FPR?

[MCSRHelix]

sorry, I forgot to mention it has the correct fuel pressure. Ive been trying to diagnose this issue for a couple months now and I too am still leaning towards the IACV, However it occurs consistently; there is no intermittent failure(several hours of observation). I'm curious if you know what happens when I unplug the MAF. Does it go into a limp mode that causes the car to run off a default map and ignore all sensors? I have been able to read some live data via the obd1 port but this specific version of the impreza is quite rare and only some PIDs are correct, thats how I know the CTS is reading correctly. Also if you know how i'd be able to find an iacv with the correct orientation of nipples please let me know.

[MCSRHelix]

Also it seems to me that when the iacv code sets it disables an injector to run on 3 cylinders? Maybe it's way of controlling idle when it is unable to correct with the IACV?