The vacuum advance solenoid valve is part of the ignition advance and emission control system. It sits behind and below the fuel distributor and has vacuum hose connections to the ignition distributor and the thermal vacuum control valve on the coolant Y-pipe.

This How To covers a recent diagnostic sequence and the subsequent leak repair on the (original) vacuum solenoid valve on 0934.

A diagnostic intake system smoke test on our car over at mark w’s place last weekend showed smoke coming from somewhere on the vacuum solenoid. We used his Redline professional smoke machine pumping into the right rear port of the intake manifold with air filter box removed and the metering unit intake blanked off. He thought the smoke came from the electrical fitting on the valve.

Noting here that the diagnostics below can be done on the vac solenoid in case you don't have a good smoke machine and want to see if your old valve is OK or not.

The vacuum solenoid on this car is the original. While replacement units are available I opted to go for a DIY repair job to start with.

Back home I removed the vac solenoid, its connector and its 2 hoses noting which hose went to which port (see emissions label on engine cover for confirmation) and not worrying about the electrical connector polarity since it doesn't matter in this case.

I ran bench tests with the valve out of the car using a 12V power supply, a brake bleeder pump/gauge, soapy water sprayer and hoses/plugs:
1. Verified clicking sound when 12V was connected-disconnected at the two small male spades (PASS)
2. Center port held vacuum with valve activated/closed and outer port (distributor advance) open (PASS)
3. Center port didn’t hold vacuum with valve deactivated/open and outer port capped closed (FAIL) - consistent with the smoke test.
4. With outer port still capped and valve deactivated a soapy-water leak test showed bubbles at/around the electrical connector while lightly blowing into a hose to the center port proving the seal at or around the elec connector had failed.

DIY remedy
1. Prepped the face of the valve and the electrical connector base with a wire brush and parts cleaner plus an alcohol wipe.
2. Applied silicone sealant where the connector base meets the face of the valve. Also sealed the small gap between the two raised black plastic connector bases.

After the silicone cured I repeated tests 3-4 to verify PASS, then reinstalled the valve.

Sending a shoutout to mark w for the pro smoke test and further advice on this little job.