RX-7 1994 Workshop Manual, page F-137 states that the double-throttle system exists because of the "response delay of the manifold absolute pressure sensor" to rapid acceleration, which causes a lean fuel mixture. The DT "prevents hesitation caused by this lean fuel mixture by slightly delaying the opening of the double throttle valve" with respect to the upper throttle butterflies.

OK, fine. But this phenomenon of the MAP sensor delay surely exists whether the engine is hot or cold, right? So shouldn't the double-throttle system be active at all times?

But at the bottom of the page, the manual states: "When the engine coolant temperature [is] below 80°C (176°F) the PCME turns the solenoid valve ON, applies vacuum to the actuator (double throttle control), and closes the double throttle valve."

According to the system diagram on the same page, there is a check valve preventing vacuum from being relieved as the lower butterfly opens and UIM pressure rises from the idle condition. So it looks to me as if the double throttle butterflies are closed, period, until the 80°C temperature is reached. Then the PCME switches the solenoid to a vented-to-atmosphere condition, which spring-returns the double throttle butterflies to a fully-open state.

The actual operation does not seem to meet the stated intent of the double-throttle system.

Any comments or objections?

 

I think that's a copy-and-paste job from the FC service manuals. Some of the FC's, I think the automatic ones, had the double throttle working all the time. It's a bandaid for shitty 80s software in the stock ECU. Newer speed density cars don't exactly have to worry about that.

On the FD the double throttle basically limits engine torque until it warms up. It's another function that has been replaced by software in a modern electronic throttle. It's idiot proofing, and since I'm sure you don't beat on your car when it's cold you shouldn't be concerned about the system unless the butterflies are stuck closed.

 

Exactly. The primary and secondary throttle plates are staged anyway. If you open them manually, you can see the primaries will open slightly before the secondaries move. Once the car warms up the double throttle stays open. There is really no benefit in keeping the system. Just don't gun the throttle until the car warms up.