When you're having problems, the first thing worth trying is the idle learn procedure. The ECM uses non-volatile memory to keep track of the IAC position when the engine and ECM are turned off. Each car has a unique IAC value that takes into account the condition of the sensors, air and vacuum passages, etc. Whenever the ECM loses battery power (which clears the stored IAC position) or significant changes to the system (e.g. sensors are replaced) it is a good idea to perform the idle learn procedure.
The procedure in the service manual was superseded by a more recent service bulletin. It says to turn the car complete off (remove the key), remove power from the ECM for 20 seconds and then start the car. Let it idle for 10 minutes. Shut it off for 20 seconds and then start it and let it run for 5 minutes. Shut it off again and you're done.
The first 15 minutes of the procedure is to get the engine up to normal operating temperature. So an alternate method would be to warm the car up, shut it off, remove power from the ECM, and then run the car for 5 minutes and shut it off.
I've been told that some scan tools have the ability to perform an idle learn on some makes and models. This method is supposed to be much faster, only taking one or two minutes. Note that Chevrolet technical service bulletin (TSB 91-114-6E) indicates that some versions of the GM TECH I scan tool ECM cartridge will not work with the W engine.
If you have the factory service manual you can figure out that instead of disconnecting the battery (which resets the clock and zeros your radio station presets), you can remove the "inline fuel fuse." This is located under the dash on the firewall next to the relays.
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Craig Leres