1999 Toyota Corolla I can't seem to figure it out

My car had been running great since I bought it 2 years ago. Last summer I had 4 gallons of water put into my gas tank because someone mistakenly put water in a 5 gallon gas drum and forgot to tell me. I drained the tank and the car ran fine after that. About 6 months later the engine started running weird. It idles fine but when I accelerate it starts to sound like the engine is getting choked out, it sputters and then when I press the pedal to the floor it seems to "punch out" of the problem it has. I bought some iridium spark plugs and replaced my plugs. The problem was 100% immediately fixed, and I was happy as heck. But about 3 weeks later the same problems started coming back. What do you think the issue is?