You need to remove the air cleaner outlet duct and inspect the
Throttle Body bore and the throttle plate for deposits. You will need to open the throttle plate to inspect all surfaces. Then you can clean the throttle body bore and the throttle plate using a clean shop towel with GM Top Engine Cleaner, P/N 1052626, or AC-Delco Carburetor Tune-Up Conditioner, P/N X66-P, or an equivalent product and install the air cleaner outlet duct.