Just bought a 94 Vigor GS. Found out the owner never put premium gas in it. It runs great, but is this bad for the car? Can i continue putting regular in or should i be always using premium?

Bad gas causes injectors problem, may have to clean injectors soon. Better change to good gas.

When my dad borrowed my vigor he accidently filled the tank up with regular gas and then it wouldnt start for awhile so i wouldnt put regular in.