Help - 2003 Sunfire Hitching / Bucking

My 2003 Pontiac Sunfire has been doing something weird lately. My Sunfire has a standard transmission with 30,000 kms, and sometimes when I stop at a red light and push in the clutch, the motor is stuck
revving at 3000 rpm. Sometimes when idleing it will fluctuate on its own between 500 rpm to 3000 rpm. The car will also start hitching while travelling down the highway. Usually seems to occur when the weather is wet. GM Mechanic is stumped!
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The idle air control valve is a likely suspect..
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Robert Hancock Saskatoon, SK, Canada
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