That is the vacuum control valve. It controls how much vacuum is going to the transmission modulator on the trans. The amount of vacuum going to the trans is related to the engine rpm. They aren't NA specific. I actually thought they were only on the turbos, but I was wrong once, so I goes it could happen again. You should be able to find one on just about any auto trans 123. The early models were all mechanical. They had linkages that controled shift quality and timing and a mechanical modulator. Some time around 79 they must have switched to the vac controlled trans.

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