Does the purge valve supposed to click on and off while the motr runs on a 99 grand prix 3.8?

Yes, the purge valve on a 1999 Grand Prix with a 3.8-liter engine is designed to click on and off while the engine runs. This clicking sound indicates that the valve is functioning properly, allowing fuel vapors from the charcoal canister to be drawn into the intake manifold. If the valve is not clicking or remains constantly open or closed, it may indicate a malfunction that should be investigated.