Engine - Idle Speed Fluctuation

86ford20

Article No. 86-7-13


IDLE SPEED FLUCTUATION - 1.9L EFI


FORD 1986 ESCORT, EXP

LINCOLN-MERCURY 1986 LYNX

Idle speed fluctuation will occur when the throttle plate is set too low, causing the throttle air bypass valve to operate at a higher duty cycle. The ISC actuator is more sensitive to vacuum variations at the higher duty cycle
resulting in air flow fluctuations. The combination of air/fuel flow variations cause engine speed fluctuation.

Verify proper installation of vacuum lines and the tube between the air meter and the throttle body. (Adaptive fuel attempts to "learn" to compensate for leaks.) Set the "Throttle Plate Adjustment" to the 900 rpm decal specification with the cooling fan turned on (800 rpm for vehicles with less than 100 miles). Refer to adjustment procedure.

"Relearning" the adaptive fuel cells near idle will improve idle stability. This is best accomplished by running the vehicle in neutral, with the throttle air bypass valve electrically disconnected, at each of the following conditions for approximately one minute: 900 rpm - no load, 900 rpm - full load (A/C, headlights, heater fan), 1200 rpm - no load, and 1200 rpm - full load.

OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: Reimbursable within the provisions of the Warranty and Policy Manual.
OPERATION: 9500C
TIME: 0.3 Hr. DLR. CODING: Basic Part No. 9510 - Code: N4