Post Sandy gas quality

[igota21incher]

After a long search and an even longer wait, I finally found some gas for my z at*a local gas station. *The brand of gas I cannot actually recall, but was definitely not a big chain like sonoco, which I usually use. I told them to fill me up with 91. Shortly after the trip home, my SEL turned on. I immediately checked my gas cap to make sure everything was tightened properly, drove around for a little bit, the light was still on. *The next day I turned on my car, warmed her up for a good 5 min and noticed an unusually high idle rpm. With the car warmed up, the tach read 1000-1100. * This worried me, so I took the car to autozone to check the SEL code. Came back to the dreaded p0300 aka multiple random misfire. My father mentioned earlier that no named brand gasoline companies sometimes dilute their gas with water. This suspicion was confirmed by the gm at autozone. So I purchased some injector cleaner to help remedy the problem.*

This message goes out both as a WARNING and a PLEAto the z community to help diagnose my problem. Keep in mind that I have installed gen 3 intakes along with motordyne exhaust. Untuned. This never threw a SEL for the 6 months I had these parts on. Any comments on what I should do to trouble shoot and or resolve this problem will be appreciated.
Thanks!