Probally an IAC issue (idle air control) valve or caused from the AC system having an issue.. As soon as the engine is started, the IAC will move gradually, to a different position, based on coolant temperature. This is your cold-engine high-idle function. Call around locate a shop that has the old GM tech2 scan tool the IAC can be reset, check the AC operation first.. There is a drill for reseting the IAC but its a headache...1. Remove battery power for one (1) minute. Restore battery power and place air conditioning controls (if equipped) in the "off" position. 2. Firmly apply the parking brake and block the drive wheels. Start the engine, shift the transmission to drive for automatics and neutral for manuals. 3. Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes. 4. Turn the ignition key to the "off" position for at least 5 seconds. 5. Repeat Step 2. 6. Allow the engine to run for at least five (5) minutes. The correct IAC values for proper idle control will now be stored.
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