[QB93Z]

Is your secondary vacuum pump operating properly?

Turn the ignition key to ON with engine not running. You should hear a brief period of operation of the vacuum pump located below the passenger-side headlight. If it doesn't run, repair it or replace it.

If it runs continuously, there is a vacuum leak or a leaking check valve in the secondary vacuum system. Post up if this is the symptom and we can do further trobleshooting.

If the vacuum pump runs for short periods (2-3 seconds) and stops and then repeats, there is a slight vacuum leak in the secondary vacuum system.

There is a pressure switch in the vacuum system that tells the ECM if the secondary vacuum system is not operating properly. What year is your Z? Recently, I have seen two ZR-1's with bad pressure switches with symptoms similar to yours.

I recommend some more analysis before you do the plenum pull.

Jim