Engine - Stalls At Idle or During Deceleration
88ford02
^ STALL - AT IDLE OR DURING DECEL - 2.5L HSC
^ IDLE - ERRATIC OR HIGH - 2.5L HSC
Article No. 88-2-13
FORD: 1986-87 TAURUS
LINCOLN-MERCURY: 1986-87 SABLE
ISSUE: Stalls at idle or during decel when the vehicle comes to a stop, or an erratic or high engine idle may be caused by an incorrect setting of the throttle stop adjusting screw (hard stop), linkage or throttle shaft binding, TV rod adjustment, TP sensor, or 12A581 wiring harness chafing.
ACTION: To correct this, use the following diagnostic service procedures.
NOTE: Make sure there are NO SYSTEM VACUUM LEAKS before doing this procedure.
1. Perform EEC IV Self-Test. During Self-Test make sure the ISC motor is operating correctly. If service codes are present, refer to the Engine/Emission Diagnosis Manual, Volume H, Section 16 for service information. If no service codes are present, go to Step 2.
2. With engine off, check if there is any chafing or damage to the engine wire harness (12A581). Special attention should be given to the area of the ground strap attaching bolt located at rear of intake manifold. If chafing is present, refer to TSB article 87-17-3 for repairs, and continue with Step 3. If there is no chafing, go to Step 4.
3. If symptom is corrected, stop here. If symptom is still present continue with Step 4.
4. Make sure throttle shaft is free, that travel is not obstructed, and cruise control (if equipped) is not holding throttle open.
a. Idle engine at normal operating temperature. Check to make sure throttle lever is in contact with ISC motor.
b. If contact is obvious and idle RPM drops to correct "curb idle" RPM with slight pressure, a sticking or binding condition is indicated. With engine off, determine cause of sticking or binding. Disconnect the TV linkage (ATX only), cruise control cable (if equipped), and throttle cable. If idle speed has not returned to correct "curb idle" RPM, the tracking switch has failed or throttle shaft is binding because of swelled end seals or a bent throttle shaft. Fully retract and disconnect the ISC motor (see below - retract ISC motor). If throttle does NOT return to hard stop position, replace throttle body. RELEARN IDLE (Step 8). If symptom is corrected, stop here. If throttle did return to the hard stop position, go to Step 5.
FIGURE 21:
RETRACT ISC MOTOR
With engine "OFF", remove air cleaner. Connect a jumper wire between Self-Test input connector and signal return pin on the self-test connector, Figure 21.
FIGURE 22:
Turn ignition key to "RUN" position. DO NOT START ENGINE. The ISC plunger will retract in 5-15 seconds. If ISC plunger does not retract, refer to Engine/Emission Diagnosis Manual, Volume H, Section 16.
Return the ignition key to the "OFF" position, wait 10-15 seconds, then remove jumper wire and disconnect the ISC motor from the wire harness, Figure 22.
5. Check if throttle adjustment screw (hard stop) is causing high engine idle by holding throttle plate open. If it is, hard stop screw must be adjusted, (see following - performing hard stop adjustment). RELEARN IDLE (Step 8). If symptom is corrected, stop here. If hard stop was set properly, go to Step 6.
PERFORMING HARD STOP ADJUSTMENT
Remove throttle body from vehicle. Using a small punch, remove welch plug covering hard stop adjusting screw, Figure 22. Replace screw if loose. Reinstall throttle body on vehicle. Leave ISC motor disconnected from wire harness.
Start engine and let idle until engine is at operating temperature. All accessories should be "OFF". Set idle RPM by turning hard stop adjusting screw (650/675 RPM in gear-ATX and 725/750 RPM in neutral-MTX). Replace welch plug and reconnect the ISC motor to wire harness, Figure 22.
6. Check for contact between idle tracking switch (ITS) and throttle lever. If contact is present, go to Step 7. If contact is not present, it is possible that the ITS switch indicates tracking at all times and returns to the full-retracted position as engine RPM is increased. Replace ISC motor. RELEARN IDLE (Step 8). If symptom is corrected, stop here.
7. Make sure throttle position sensor (TP) is operating properly. This check requires access to voltage between EEC pins 47(+) and 46(-) using a monitor box or a break-out box.
a. With key "ON" and engine "OFF" monitor the TP voltage. Voltage should be about 1 volt at closed throttle and should increase to about 4.5 volts at full throttle. Cycle throttle slowly through its full range of operation. If signal is not acceptable, the TP should be replaced and then proceed to Step 8. If signal is acceptable, idle engine at normal operation temperature, monitor TP voltage. Voltage should be steady at about 0.9 volts. Wiggle ISC motor wiring and tap the TP lightly with a screwdriver handle. If voltage and RPM are steady, go to Step 8. If voltage is unsteady or idle RPM becomes erratic, replace the TP and then proceed to Step 8.
CAUTION: If battery or EEC processor has been disconnected for any reason, or vehicle has been "jump started", it is necessary for vehicle to relearn idle.
8. Relearn proper idle as follows:
a. Set parking brake and block wheels.
b. If vehicle is equipped with automatic brake release, disconnect vacuum hose and plug it.
c. Bring engine to normal operating temperature with accessories off.
NOTE: Only a tachometer is needed. Make sure there are no vacuum leaks.
d. Engage the transmission in Drive (ATX) or Neutral (MTX) and idle engine for 120 seconds. Idle RPM should return to specification (700 RPM-ATX or 800 RPM-MTX).
e. Lightly depress and release the accelerator. The engine RPM should return to specification. If the RPM remains high, repeat Step 8. If engine RPM is now within specification, make sure symptom is corrected and return vehicle to customer.
OTHER APPLICABLE ARTICLES: 87-17-3
WARRANTY STATUS: Eligible Under Basic Warranty Coverage
OPERATION: 880213A - Includes Quick Test, inspection, repair and retest
TIME: 1.5 Hrs. DLR. CODING: Basic Part No. DRIVE - Code: 95