Right now I have chevron 93 octane in the car. I tried putting the r-16 back in, the sound was still there, but the car was even slower.... I seriosly think its something with my spark plugs or ignition system, because when I set the fuel setting back to normal, the car ran fine... a little slower than before, but quite a bit faster than with the fuel enrichment on, I suppose I will get the alternator, distributor, and spark plugs checked; I might as well just get a spark booster too...