I don't know anything about Fieros, but if the car seems unpredictable the first thing I'd check for is a dead shock. Assuming you've already checked for obvious loose bolts, etc. Take 'em out, put one end in a vise and then push and pull them thru there full range. What you're looking for is smooth even resistance. If there's any dead spot where the shock moves without resistance, there's the problem. I had a similar problem with my ITA RX-7. It would push one moment and then go loose the next all in the same sweeper. It's at least worth a try and won't cost anything.