No, vaccum is not used as an indicator of load (I am not sure what you exactly mean by load) but rather used for control of various mechanical valves. And a useful indicator of the functions within the engine, because only if these functions are normal, you get certain values of vaccum.

The air flow sensor just tells the fuel injection computer how much air is flowing to the engine, and the fuel injection computer can then adjust the air/fuel mixture accordingly. More air will flow as you press the gas pedal. The throttle valve when opened, will pull the air sensor plate down and more air will flow thru the intake. The pulling of the sir sensor plate very much depends on vaccum in the intake. If the vaccum is low, you will not have a good throttle response, lots of hesitation.

There are a lot of electrically controlled vaccum valves, they let vaccum pass thru them when activated by some voltage. These valves can be used to control vaccum flow electrically and hence control various vaccum controlled valves. The ignition control unit uses vaccum for correcting the timing of electrical pulses going to the coil. Vaccum, I think is also used for some control of transmission functions.

Vaccum is a key element of even the most modern car.

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Saumil S. Patel