Cutting out

I have a 99 Mercury Villager, (163,000) miles: Out of the blue it started to sputter, and cut out when it was raining. We took it to a mechanic, and he checked it for us, said it needed new distributer cap, rotor and spark plug wires. So we changed all that, (note)(no codes or lights were on before that) after changing the sparkplug wires, the "check engine light" came on, and the van was still ideling below 1000 rpm's in park, then it would begin to jerk the van back and forth a bit, and idle rough, then we took to another mechanic he checked the codes, said the cylinder #2 code came up. Do we have a bad fuel injector, or bad wire? We didn't change the plugs cause the first mechanic said they were fine. My van continues to run ok on the highway with some jerking motion(hesitant), but when you come to a slow or stop it will idle below the 1000 rpm's and start the girking motion again. We are planning a trip out of state in a few days, and need some answers. Do we get it put on a machine to tell us what we may already know? Or start doing process of illimination with wires, injector, or? Please help. My husband thinks we may have gotten bad gas and it may have clogged the injector or something? Could that be the cause of all this? Please advise.