have you tried fuel injector cleaner? if so have you checked to make sure the #2 injector is well grounded? maybe at low rpm there is too high of resistance and the injector isn't spraying. I'd also run a compression test because if you have a slightly loose ring or valve in #2 then at low rpms it wouldn't fire. I can't think of anything else that would be specific to a single cylinder. hope this gives you some ideas to start on.