Never have had this problem, but unless the gas had water in it, it shouldn't make a difference. The car is equipped wiith a anti-knock sensor that should quell those pings and knocks. It may, however, make a big difference over the long haul. The car requires premium fuel, period. I know in this time of inflated gas prices it's tempting to dump cheaper gas in it, but the real dollar savings is minuscule compared to what you leave behind in your engine. Decide on a decent brand of gas with cleaners, and stick with it. I use Amoco. That's my advice.

Obviously this could be related to something else, but you haven't completely ruled out the gas being contaminated...
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John Shatzer, '97 V90 @ 94K