1993audi90cs

my buddy has a 2001 audi a4 2.8quattro and he said his engine just started sputtering the other day at low rpms when its idling and when he steps on the gas it cuts out enough to be noticed. i told him it might be the plugs. so he pulled one quick and he said it had oil on it, and his check engine light has been coming on lately. im guessing it needs more than just a tune up with plugs and wires but i need some help as to what else it could be.