How do you adjust the cold start idle speed on a 1991 Toyota Camry 4 cylinder gasoline engine (3S-FE)?
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The idle speed on the 3S-FE is computer controlled. That is effectuated by a bimetal termal valve on the bottom of the throttle body (part of the Idle Speed Control unit). I trust you have done a cleaning of the throttle body with emphasis on the idle air control passages (big hole just in front of the throttle plate). Make sure that coolant is flowing to the ISC through the little hoses below the ISC. Finally check the resistance of ISC1 and ISC2 windings to see if they meet specification.
If someone has messed with the throttle plate stop screw, set that back to the specified minimum air clearance of the throttle plate.
Hope this helps.