[A26B]

Sounds like you have a vacuum leak, likely in the Secondary Port Throttle (SPT) System. There is a rubber hose connection, near the alternator, in the hard plastic line from the vacuum pump to the SPT system. Disconnect the line there.

Key on- Engine off, put finger on end of hose going to the vacuum pump to isolate the pump from the SPT system. The pump should only run a short time and stop until you release your finger. If this is the case, the vacuum leak is in the SPT system. Re-connect the hard plastic line.

Before removing the plenum, Remove the vacuum line from the pipe located on the driver side of the plenum at the center. Key on, Engine off, plug the removed hose. If the vacuum pump stops and/or the stop cycle is significantly longer between starts, the problem is likely the check valve under the plenum is faulty. If not, then the leak is under the plenum.