Where is the idle adjustment screw located on a 1989 ford aerostar van?

The 1989 Ford Aerostar doesn't have a readily accessible idle adjustment screw in the same way many older carbureted vehicles did. The Aerostar uses electronic fuel injection (EFI). Idle speed is controlled electronically by the engine control module (ECM) and is not manually adjustable with a screw.

Any attempt to adjust the idle speed using a screw would likely be on a component like the throttle body, but adjusting it would be incorrect and could damage the system. If your Aerostar is idling too high or too low, the problem lies within the EFI system itself and needs professional diagnosis. Possible causes could be a failing throttle position sensor, a vacuum leak, a problem with the ECM, or a dirty idle air control valve (IAC).