How to prevent car from stalling

I have a 99 buick regal 3800 non supercharge. I changed the plugs and wires a couple days ago and the following day I added fuel injector cleaner. About 24hrs later I noticed that the engine was reving a little higher than normal. I don't remember how much. Then yesterday it was still reving high and when I go to accelerate from a traffic light it would sputter like it was going to stall so I let off the gas and it wnt to normal including the rpms. Today my fiance was driving the car, and taking me to work and we noticed that when we came to a red light and started to slow down it would rev real high and then drop suddenly and stall and is still doing that. I had her take it to oreilly's auto parts, cuz they do free obd2 scanning and we got the following codes. P0102, p0137, p0440. Any help in this matter would be greatly appreciated.