1991 Oldsmobile stalling/accelerating and poor idling problems

I have an 1991 Oldmobile Cutlass Supreme and it started with stalling problems when coming to a stop (stop light/stop sign). I brought it to a mechanic and he replaced the IAC. This didn't resolve the problem so I brought it back. This time they exchanged the spark plug wires but this also didn't solve the problem. Another problem occurred together with the stalling, the car would accelerate by itself. Again I brought it back to the mechanic and this time they replaced the fuel injector, they also told me they checked the TPS, the cadillac converter, and they suspected a vacuum leak but weren't able to find it. They gave me the car back without fixing the problems. Even more and more problems occur, after paying several hundred of dollars the problems didn't get fixed. At this time the car will idle very poor, while pulling plug wires one at a time found that with two of them OFF it made no difference in the idle. Is it running on 4? It will still stall at a stop and accelerate by itself. Also it's hard to come to a stop. Does anyone have any ideas/tips on what could be wrong with this car?

Welcome to AF, what engine number one, second kinda tough to jump into the middle of a misdiagnosed issue, many things can cause this, if you can find that 2 cylinders seem not to fire I would have back at the shop and let them pick it up from there.

So the money spent on these ineffective repairs is lost/gone. I would not let that happen . Anyway, Try cleaning the egr/and disconnecting it for test purposes, also get a vacuum gage on it to see whats what.