What the problem is?

Sounds like youre having bump-steer. That refers to the change in toe (in or out) as the suspension travels over bumps. Bump-steer is made worse by having 94-95 spindles with your 89 outer tie rod ends.

You can improve it in one of four ways:
Your spindles have a straight steering arm, which aggravates bump steer.
96-up spindles have a curved steering arm, but they also widen the front track width, which may cause problems with tire to fender contact.

91-93 tie rod ends are better with bump steer than the older ones, and they will bolt on.

Offset steering rack bushings will raise the rack, instead of lowering the outer tie rod ends.

A "bump-steer kit" is a special pair of outer tie rods with spacers to lower the attachment point of the rod end, relative to the spindle.

My 90 has 94 spindles and it was terrible (required two hands on bumpy roads) until i got the bump steer kit...i eventually installed poly rack bushings too but i was able to get away without using the offset ones. YMMV

Hmm, let's see...
MY kit came from Ford Racing, but it took way to long to get here for my taste.
Like a month or two and it wasn't even Ford, it was made by HPM Motorsports.

So, I would suggest Steeda, Maximum Motorsports, or UPR.
http://www.steeda.com
http://www.maximummotorsports.com
http://www.upr.com
Summit should have one or more of these in stock.
http://www.summitracing.com
They are usually ~$149 + shipping, and you will (obviously) need an alignment afterwards.

BTW, do you have caster/camber plates installed? They will help too, since bump steer is worse if your alignment is off (or stock )

Also, I used my 90 V8 struts i had just installed...with a 2.3 engine lol
The caster/camber plates will have spacers for different length struts, to keep them from bottoming out.
And I forgot to ask if your car is lowered.