Sure sounds like a fuel problem, and water/ice in the fuel would be my first guess. Also make sure that your fuel tank vent tube isn't (partially) stopped up. Have you checked the fuel pressure?
Yes, you can. Most of those additives are mainly alcohol, and that can do bad things to a fuel system. The best thing would be to empty the tank completely so you'll only be dealing with what little fuel is still in the EFI system. Then use the recommended amount of HEET (or whatever brand of water remover). I like Sea Foam as mentioned above, but I don't think it does as good of a job at specifically removing water (assuming that's the problem).Can i harm my engine if i use to much fuel antifreeze?......