Idles way too fast (Or occasionally too slow)

First, if the computer and MAF were replaced with no results, then they owe you a proper repair unless you signed for the replacement of those parts, shooting in the dark, so to speak. If they guaranteed their estimate and work, you shouldn't have had to pay for that. if you deal with a fly-by-night shop, then it's on you. A good technician would have fixed your car or not charged for the repair. Enough lecture.. I'm suspicious of the throttle position sensor and I have another couple of vague ideas, I'd have to diagnose the car to see what's wrong. Find a GM specialist to help you. Your car is not so complicated that it should be a big mystery to a good tech. Here's a directory link for you: https://repairpal.com/oldsmobile-repair-in-green-bay-wisconsin