Studdering 3.1

I'm a backyard mechanic and I'm tring to find out what's going on so here it is= car in studdering and no power, changed all plugs (nasty white powder on all but #1 cylinder looked normal owner told me he has been using gas from his work and they have had problems with water in the fuel, put new gas in) and wires and vacuum line going into intake, it runs better now but still studdering I checked all the plugs again, they look good, checked coil OK fuel fliter changed, egr