Also how about the “restrictor plates.” The ones with two smaller holes in them that block the air. Are those supposed to do the same thing as the “adjuster” except ones adjustable and the other isn’t? Or are they two different animals?
I dont have any experience with the use of a restrictor plate,but going by the image & reading its description,its main purpose appears to be for the prevention/reduction of a hanging idle that occurs between shifts & when in neutral,like when coasting and slowing down.BTW- the idle is supposed to hang when the clutch pedal is down or the shifter is in neutral,when the car is slowing down for a stop or shifting.This is because of the idle dashpot function.I suppose if you want to cut the high idle off a little earlier than what the ECU is commanding it to do,the restrictor plate could be used.The plate supposedly reduces the airflow to cut the idle hangup off quicker.The following description is listed for a plate on Ebay.
** This IAC Restrictor Plate restricts the incoming air to the motor between shifting, and going into neutral getting rid of that RPM hang up.Drops that RPM hang up with (2) size Restrictor holes you can custom tune how fast you want the RPM to drop**
If you wanted to try the restrictor plate method,you could make one of them with a thin piece of sheet metal.Just set your iac valve on top of a piece of it,trace its outer flange shape and its mounting holes onto the metal,then cut it out with tin snips and drill the mounting holes.Then drill two different sized holes,in whatever diameter is shown or listed in an ad for one of these plates,then mount it and try it out.
The iac adjuster plate is different in its shape and function.Its used to increase idle a controlled/precise amount if the throttle body is built up with crud or if a rough/low idle is occurring due to a aftermarket cam and it can also cut bypass air off to lower idle too.