If your Fiero is an 88, the alignment is set by the position of the cross shaft that holds the upper control arm.
The two bolts that hold the cross shaft are bolted through slotted holes in the front cradle, next to the spring pocket.
The position of the cross shaft can be changed by loosening the bolts, and moving the cross shaft around, to different positions in the slots.
I have had several instances of the bolts being loose, and allowing the control arm shaft - and control arm - to "walk around".
It usually happens when you change directions (forward to reverse, or vice versa) and then turn the wheel or stab the brakes.
It usually makes a solid "thunk" noise under the car when it happens.
If it's an earlier car, the alignment is set by adding or removing washers on the upper control arm shaft, or by rotating the upper ball joints.
If that is what is moving around, I'm thinking worn bushings or worn something else.