My 1998 Isuzu Rodeo will not engage when I push the button. The 4wd light flashes continually. I have vacuum on one hose at the actuator. The vacuum unit on the fire wall will not switch states. What could be the problem.?

SOURCE: 1999 isuzu rodeo 4wd not woking

I had this happen to a 1999 4x4 LS and my sisters boyfriend mentioned to periodically turn 4x4 on/off at least once a month.
What I did was go down a stretch of road slowly and attempt to turn it on/off till it became unstuck.
Drove around 10 miles on a road that was hardly used...to get the stupid light to quit flashing I had to put it in park and try to creep forward ---while using off settiing or put in park then reverse...while using the off -setting on 4x4. My patience paid off. They get sticky...you must be cautious... because there is a way to cause vibration and then it won't start...some deadman feature that I experienced once and the LWD must have slipped in a little and I had to look at everything.
Mine is an Automatic with the shift on the floor...that can get sticky too.

Good luck and hope this helps...mine had lots of growing pains but I get 23 mpg and it runs/idles better and the only gremlin left is some short in the dash which leaves the lights D/3 (one or both on)for the shift indicator on:)