Power steering

[Xoloski]

98,  for sure, no such car in 88,  unless stuffed into a Samurai.

that is  hard question,  but  check ball joints and struts and tie rods.

for sure a mechanical problem up front, and intermittent is more strange.

find  suspension shop to check it out? is best,  look for loose parts. upfront. (if part is real loose it can jam)
they will put  it on a lift and float the front end and check for loose and binding parts.  all parts up front checked.

 Thanks WB,
I will put it on a lift, release the pitman arm and inspect the entire system and post my findings.
For some reason I suspected a pump issue / pressure valve or switch issue and not a mechanical bind issue. 
and, you are right, this unit is a '98. My 1st sidekick is a '93 and my Samurai are 86 white, 86 blue, 91 black.
Xoloski