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Old 04-26-2010, 08:36 AM
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MT-2500 MT-2500 is offline
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Re: 91 GMC rough idle

If the only problem is idle work on and check IAC valve sndIAC valve control.
The PCM and iac valve should hold idle upto specs.
Also make sure pcv valve is ingood shape.

What RPM is it holding in park and drive?
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