While this is my 5th fc it is my 1st A/T.
When the engine was out and I was going over and replacing emission equipment and all vacuum lines I noticed that the double throttle diaphragm has an extra input. This input simply connected to a vac source with a slow release valve. As is to be expected the diaghragm was shot so I capped of the whole system.
My hypothesis is that the extra vac source allows the secondaries to open slowly even when the water temp is cold. I just don't understand why it is only on the A/T. Anybody want to explain mazda's reasoning for a more complicated system.
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The MT has a double throttle diaphram also, but it is a single diaprham where the AT has a double unit. In both cars the diaphram actuates the first double butterfly throttle valve, which is upstream of the secondary throttle butterflies. Its purpose is actually to act as a choke, enrichening the mixture when the car is cold. The thermovalve allows vacuum to close the valves as long as the car is cold. When it warms up, the thermovalve vents the system to ambient, and the valves open. The delay valve is present in both cars, but the delay is different in the MT vs the AT. I have found no expanation for that.