Your looking for the throttle kicker solenoid. It controls vacuum signal to the idle speed control (ISC), a vacuum actuator/motor, on the left side of the carburetor. The hose connections to the solenoid are manifold vacuum and the ISC actuator. The solenoid is controlled by the ECM. And, you are correct, that is a 4.3L-V6 engine. To my knowledge ISC was used for California emissions on non-A/C equipped V6s, only. Check with a local Chev/GMC dealer for a part number (P/N) and have them run it on their national locator network for a dealer that might have NOS. Otherwise, Google the P/N.