it all seems unnecessary to me, but that's nothing.

my last 80s mazda 4 banger (and this thing had as much torque as a 305 chevy, it was a really stout little 2.2l motor) was a hybrid fi system, it was port fuel injected, it had a full on long runner high pressure multiport fuel system with a bigass monoblade throttle body. but it had a vac advance distributor......

anyway this thing had a bank of a half dozen vacuum solenoids and sensors mounted on the firewall, with all these crazy vacuum lines going everywhere, with tees, check valves, hard lines, totally nuts. probably 20 feet of vac line.

this crazy squid-looking device was linked to every damn system either electrically or pneumatically.. steering, hvac, distributor, egr, a/c, headlights, whatever. there were at least 6 vac lines running just to the throttle body for both pre and post throttle plate air control.

anyway i only found out when i started having issues with it, that the entire point of this system was to stabilize idle by allowing extra bypass air when an accessory of any kind, either electrical or parasitic on the rotating assembly, was turned on.

each solenoid even had a knob on it to adjust the amount of air that was added for each accessory bank. you could tune this thing so it would respond to the defroster being turned on by raising idle 1000 rpm, or not at all.

the funniest part is it had computer controlled IAC too, so all this stuff was totally unnecessary, if they just would have put some damn contact switches in place.

crazy stuff....