I'm not sure if it's the same problem, but at about 100,000
miles on my Seville it started to have a similar problem. If I
was lugging the engine too much in 4th gear, particularly
going up a hill the torque converter (I think?) would unlock,
causing my RPMs to run higher. Like if I was cruising at 60,
instead of running at 1600, it would run at at least 1900,
sometimes more. My "solution" was to not lug the engine --
to kick it into 3rd heading up hills. That doesn't account for
any strange super-high idle, though, especially because
generally taking my foot off the gas actually caused RPMs to
dip BELOW normal, maybe 1400 or 1300 at 60.
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