1989 930 Rebuild Vacuum switch question

[CreatuR]

What is it, what does it do and do I need to keep it? (part circled in red). Thanks!!

[JFairman]

That vacuum solenoid is origonally in the vacuum retard line going to the vacuum retard pot on a late eightees USA 930. Thats the pot closest to the distributor.

It usually has a blue hose instead of a red one on it going to the distributor. the other hose is on the bottom left fitting on the throttle body like your picture and thats correct.

Blue hose was used for vacuum retard and red hose was for vacuum advance on 86-89 USA cars and maybe other catalytic converter/air pump 930's too.

It's purpose was to block the vacuum retard signal to the distributor's vacuum retard pot for the first couple minutes after a cold start and doing that would make the timing advance somewhere around 6 degrees and the idle would raise about 300 rpms. It would be getting 12 volts from the k-jetronic box to do that.

Then after a couple minutes the k-jetronic box under the driver seat would cut the 12 volt supply to it and it would open and let the vacuum retard signal go to the distributor and the idle speed would abruptly drop about 300 rpms as the timing was retarded.

By itself it's kind of like a SPDT switch because it can be used 2 different ways depending on how the hoses are hooked up to it and which outer one is vented to atmosphere.

There were origonally 2 of them side by side and the other one operated the 2 air pump diverter valves. They were both wired in parallel and were triggered by the ECU at the same time.

You don't need it but if your ignition timing is stock it will help along with the auxillary cold start TB air bypass valve to keep the idle up when the motor is cold and also help the emission controls work as designed.

[CreatuR]

Thanks for the outstanding post and information!