F 250 4WD Pickup V8-302 5.0L (1986)
Idle Speed: Adjustments
CURB IDLE SPEED ADJUSTMENT
Explanation
Curb idle speed (RPM) is controlled by the Electronic Engine Controls (EEC IV) processor and the idle speed control device. If the control
system is operating properly, these speeds are self-compensating and cannot be changed by traditional adjustment techniques.
Adjustments are sometimes required to establish the correct operating limits within which the Idle Speed Control (ISC) system can properly
function. Misadjustment of the operating limits could restrict the operating range of the ISC system, so adjustments to the system should never
be made unless a specific causal factor has been identified.
Procedure
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Set parking brake and block wheels. Place the transmission in Neutral/Park.
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Bring the engine to normal operating temperature and turn off.
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Turn the A/C-Heat selector to the Off position.
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Verify that the throttle linkage is free, that travel is unobstructed and that the cruise control cable (if so equipped) is not holding the throttle
open.
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Check for vacuum leaks.
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Place transmission in Neutral and operate engine at 1800 rpm for at least 30 seconds.
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Place transmission in Drive (A/T) or leave in Neutral for (M/T). Allow engine to stabilize and check idle speed.
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If curb idle speed is equal to less than 675 rpm (A/T), 775 rpm (M/T) do not adjust.
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If speeds exceed 655 (A/T) or 775 rpm (M/T) turn engine Off and disconnect the positive (+) terminal of the battery and then re-connect.
Repeat three previous steps.
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If speeds exceed specification, perform EEC IV Quick Test and resolve any indicated defects. See: Powertrain Management/Computers and
Control Systems/Testing and Inspection
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If speeds still exceed 675 rpm (A/T) or 775 rpm (M/T):
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Back out idle air set screw until the idle speed reaches 600 +/- 20 rpm (A/T) or 700 +/- 20 rpm (M/T).
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Then back out the curb idle screw one-half additional turn to bring the throttle plate linkage into the nominal operating range of the ISC
system.
