In the '99 A4 brochure, Audi recommends using gasoline with 87 octane, with 91 for maximum performance (for the 1.8T). I have read numerous things about A4 owners having problems with their cars that appeared related to the type of gasoline used. How sensitive is the 1.8T to various types of gas? Has anybody had problems that could definitely be traced to "bad gas?" And if so, what made the gas "bad?" The octane, or the unknown origin of the gas (e.g., not "name brand" gas?)

I have (to this point) run only premium unleaded in my A4, so I can't comment on how lower grades of gas fare. I can comment on my old, beloved Jetta GLI 16V 2.0 that insisted on premium when operated at lower altitudes. At our local altitude, (3600 ft) there was never any problem using whatever grade, although I always defaulted to the premium. Knowing how a turbo would be more likely to cause detonation makes me a little leary about cutting corners on fuel.<p>If you run 5000 gallons of gas through your car (100,000 mi @ 20 mpg) and save $0.10 on each gallon, you would save $500 over the life of your car. An engine rebuild caused by detonation would probably cost 5-10x as much, all totalled.<p>Personally, I think it's cheap insurance. Plus I use injector cleaner regularly.<p>Naturally, YMMV ;-),<br>Steve (the OTHER Steve M)