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Welcome, I'm Chris (aka Moose).
The IWEs work by being locked in with no vacuum and unlocked with vacuum. It should only take 6 inhg of vacuum to keep the IWEs unlocked. If you are not getting this vacuum to the IWEs in 2wd and while running then you have a leak or a concern with the IWE solenoid. If you apply vacuum manually to the IWEs and it holds and still will not unlock then the IWE or the gears on the shaft and hub are damaged.
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With the vacuum to the IWEs, when the front tires roll if the axle shafts are spinning then there is a concern with the IWE not allowing it to unlock.