It is barely running. It surges when it idles, won't run above 3500 rpm, looks like gas is coming out the tail pipe, and dies anytime I let off the gas when driving. I mixed leaded 110 ocatane in it at the track last night along with my 93 ocatane. The car started acting like I described after a few runs. Could I have toated the oxygen sensor? Could it be anything else? Thanks.