In my experience, by itself, Venturi-vacuum is not strong enough to open the EGR-Valve . This signal is very small; especially on a 4-cylinder. Which is why engines that use this system also need an amplifier.
The control system inside the amp, varies manifold vacuum to the EGR, in direct response to the varying Venturi-vacuum, locking the two together; so that the signal out of the amp is always proportional to the signal from the V-port. Thus, you can plumb a vacuum gauge to the output signal, and watch what it does as you vary the input signal. The amp is essentially a vacuum relay, much as is your brake-booster, with the two sides fully isolated from eachother with no signal at the Venturi.
And, the amp has to be sealed from atmosphere at all times.
On a Mopar EGR valve, you can observe the pintle rising and falling, thru the metal bridge. Sorry. IDK anything about your Mazda valve.
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BTW
For a street vehicle,
EGR is not the bane of performance, that some guys preach; the gas is inert and contributes nothing to the combustion process, except to cool the mixture during the burn, to prevent formation of NOx, a so-called pollution gas. Heat makes pressure, makes power. Therefore, this addition of EGR-cooling, reduces power.
Therefore, to compensate for the Part-Throttle power loss, the throttle has to be opened further to get whatever power you are looking for.
After you reach a certain throttle opening, and are no longer at Part Throttle, you will want full power, whatever the engine can produce. At that time, you want the EGR to drop out, to get the heat of compression back, which is then amplified by the burn.
Venturi- vacuum is a good trigger to use for this. When it is working correctly, you might never know it's there.
However, the actual controller in all this is the vacuum chamber on top of the valve, which is spring loaded, which gets old and tired, and eventually will allow early activation of the pintle, which then, you get the kind of issues you are talking about.
But with a Mopar valve, the usual failure is a ruptured diaphragm, which then presents as a vacuum leak to the engine, and you get a different symptom.
In a 318 Mopar, that crossover usually cokes up and no longer passes EGR at all. Which IMO is fine lol, except now you get different symptoms;
1) the carb is slow to warm up as the ambient temperature drops, and so, the choke stays on way too long, and
2) and once the carb warms up, all that hot coke under the carb, can cause hot-running issues
And don't forget, that pesky heat-riser valve, whose job it is to divert that hot exhaust up under the carb, cuz most of those systems also have a heated carb/ heated air intake, both of which are designed for a quick warm up, and an inlet air temperature that is calibrated to work at a specific temperature at all times........ except at WOT, then those systems drop out, just like the EGR does.
The End Goal is that at or near WOT, the engine is always supposed to give you all that it was designed to. If it's working right, it is supposed not to affect power whatsoever.
But it will cost you a lil fuel mileage at low throttle openings, after the engine is warmed up, especially on low-compression designs.
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IMO
In it's day, it was a pretty impressive bit of engineering, so long as it worked.
Over the years, the very modest amounts of EGR, grew ever larger, as EFI and Ignition controls evolved. But the fact remains that simultaneously, mechanics evolved to figure out ways around it. Sometimes this is Good, and at other times, not so good.
