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2004 gmc
26,436 Posts
You have a good challenge, all right. Fuel pump getting old - low pressure? How many miles on her? Plugs changed at 100K if it's over that? Ignition switch could be flaky, especially if it works every other time. Starter cranks, but the ignition could be suppressed during cranking by a bad switch that has a problem in RUN/START mode. Excess fuel injected gets burned off after it lights up, causing the high idle? Can you check the PCM data for ECT? Excessively low ECT could engage the high idle table until it thinks it's warmed up.

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