Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Check if the throttle body is actually loose or the base gasket is bad. Grab the throttle body while the engine is idling and try to move it as hard as you can in a 4 directions. If the idle changes, check the bolts for being loose and if the bolts are good, replace the base gasket.
If this isn't the case, try searching for a vacuum leak. Be careful if using starting fluid, don't spray it anywhere near the exhaust manifold.
If neither of these work, perhaps there is some dirt in the idle circuit. Let me see if that has an idle air control or anything like that that can be removed and cleaned or replaced. BRB.
Do you know if the "idle stop screw plug" has ever been removed?
Remove the idle air control valve and clean out the passage in the throttle body using some carb cleaner or compressed air. Here are some instructions for putting that valve back on, make sure the distance that the valve extends (from the motor housing to the end of the cone); the distance should be no greater than 11/8 in. (28mm). If it extends too far, damage will
occur to the valve when it is installed.
If that don't' work, try removing that idle stop screw plug and adjusting the idle per these instructions,