I appreciate your replies, here's my explanation of the circuit using the 1st .png file, which is the same as the .asc file, The oscillator in use has an 8 hz triangle out put (the 1uf should be 3 uf), it is the mixed with the speed setting and separation setting and a balance setting to give me 2 triangle waves that are separated 1.4 volt and balanced to the amp-out signal. The LM2907-8 frequency to voltage converter is fed with the tach signal from the engine and varies accordingly. The amp-out signal is compared to the two triangle wave form to give me a PWM out put to the vac FET or the Vent FET which opens and closed the valves accordingly. The PID would be applied to amp-out signal from the frequency to voltage converter to make it slower acting.
I attached another .asc that has fixed settings. If you run it, look at upper, lower, and amp-out, then change the frequency of the sine generator and also look at how it effects the vac and vent signals.
This is being used on an off road vehicle, so there is no standard for it, and I started with a vacuum actuated unit that has enough power to move my throttle, even though the new model of the same thing is electric.
If you break it down, by chips, it's quite simple, oscillator, mixer separator, f to v converter, comparators, drivers and voltage regulators (the 12 regulator is more stable than the supply and 8 volt is plenty of voltage for the valves without making them hot.
Thanks
Kinarfi