94 nissan quest has started idling at 500 rpm. I

Jeff did you figure this out. I am dealing with the exact same thing currently. Things to look at are Mass Air Flow Sensor (MAF), Throttle position Sensor (TPS), Air Idle control valve. I have played with everything but the Air control valve. I tried three different MAF, including a ghost sensor (circuit to match ressitance). I'm going to investigate the air idle control tommorrow. Let me know if this helps or if you get it figured oot