| The AAC is controlled by the ECU to maintain idle speed under different conditions. If it's not working you will have poor idle control once it's warm (or stall when cold if the Air Reg is also not working). Pull the connector from the AAC and clean the terminals. Using 12 volt power from the battery, touch + and - to the terminals momentarily and notice if you hear a click. If nothing then most likely the AAC solenoid is shot. Could also be plugged but they do go bad sometimes (I've had 3 die over the years). If you remove it make sure to use a new gasket otherwise you can have a massive vacuum leak.
If it seems ok then clean the terminals on the connector and set the idle. Warm the engine to operating temp, turn the idle screw on the side so it reaches about 650 RPM, then plug the connector back in. It should immediately rise and then settle at about 725 ~ 750 if it's working properly. The Air Reg has a disc inside controlled via a bi-metal spring which closes the disc when it's had power for a while and warms up. At cold start it's open and allows more air into the plenum so the idle is increased. If it's plugged shut it won't work and you will not have cold hi-idle. If you take it off you should be able to see through it. If not, disassemble it and see if it's clean. By connecting 12 volts to it and leave it for a couple of minutes it should rotate the disc closed. If not, it's NFG.
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