Quote:
Originally Posted by L.Fite
LOL... ok so that explains what it is...
But why did the engineers decide it was needed originally?
Still curious...
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With an IAC, all idle rpms are consistent. You start your car up when its 0 degrees outside, the car instantly idles at 900 RPM (or whatever).It will stay at 900 all the way through the warmup process. No need to stomp on the carb linkage to keep the choke from reving 2000 RPM in your driveway as it warms up. When you turn on or off the AC, it still stays at 900. When you go from park to drive, 900. If the engineers decide they want 1000 rpm when the air conditioning is on and in gear, but 750 when its out of gear (or vise versa), they just readjust the idle rpms in the program and the car will do whatever they want. If your in a stick car and you have to lock up the breaks at a streetlight, the IAC will catch the situation and not the the car die. If your tugging on the steering wheel and the power steering pump is binding up the engine, the IAC will keep the RPMs exactly where they need to be. With a carb, you needed to set the idle up higher to catch a lot of these situations, no need now, set it as low as you want. I'm sure somehow it saves gas, as it all adds up
There was also something to do with the emissions. I cant remember all the details, but the engines needed to idle faster while getting the 02's up and heated ( they don't work when their cold) so the closed loop could handle the emissions issues. During that short "heating period" time the emissions went out of wack. So they "Idled up" for a few seconds on a startup/restart to keep the emissions down during that short period until they switched over to Closed Loop. Usually around 7 seconds