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That is VERY extreme. Check the TPS, make sure nothing is sticking, try that. Next try unplugging the MAP sensor and starting up, see what happens there.
Are you getting an engine light? I think there is a way to pull the codes from it.
Its just a shot in the dark, but I had a friend with an 86 S-15 that had a similar problem and it turned out to be his MAP sensor gone bad.
It could also be the TPS, but I doubt an O2 would make the idle go that high.
Its just a shot in the dark, but I hope it helps.