Need Help With CRAZY ERATIC behavior

My 97 LXI 2.5l v6 has this stalling, sputtering, coughing issue. I replaced the MAP sensor because it was throwing 7 different codes. When I replaced this I no longer had any more codes but the same issue. Well I loosened the gas cap and for like 2 hours she ran beautifully and still had the dying thing when at a stop light unless you drove two footed. Now back to same problem. I waited till late last night and fired her up and disconnected the front three spark plug wires still ran the same no diferential when those were off, so I'm only running on 3 cycl. Also no bright blue spark. Going to replace Crank sensor, and do tune up tomorrow. Wondering if you know of any other possibilities. I bought this car from an individual and she locked herself out and lost the key so they had to have someone come out and cut a new key to the car. She said thats when all the problems started. Could that have something to do with its erratic behavior?