The IWE in 4wd with not have vacuum at the actuators, FYI. I found this
Operation: In 2WD mode, vacuum pressure is applied to the IWE actuators, disengaging the front wheel hubs from the half-shafts, effectively keeping the vehicle in two-wheel drive. When 4WD is engaged, the IWE solenoid reduces the vacuum pressure, allowing spring-loaded mechanisms in the IWE actuators to engage the front wheel hubs with the half-shafts, thus providing power to the front wheels.
To me it sounds like the transfer case mode actuator is not working, here is the location so you can remove it and then work the controls to see if it moves to confirm the failure. Check out the images (below). Let us know how it goes.
Image (Click to make bigger)
Friday, November 17th, 2023 AT 6:27 PM