Ranger 4WD V6-245 4.0L (1991)
Idle Speed: Adjustments
With 90TF-AA Throttle Body
*** UPDATED BY TSB 9111B4, 6/14/91; TSB 9025B2, 12/90
NOTE: The curb and fast idle speeds are controlled by the Engine Control Assembly (ECA) and the Idle Speed Control Bypass Air Valve (ISC-BPA).
The ISC-BPA valve is not adjustable. A large increase or decrease in closed plate airflow from the calibrated level will not allow this device to control
the speed.
REMEMBER
A change in idle airflow can occur not only at the throttle body, but other areas as well. You should enter the idle speed procedure only after other
possible causes in the following areas are eliminated.
^
Contamination within the idle speed control device
^
Lack of fuel system control (excessively rich or lean)
^
Throttle sticking or binding
^
Engine not reaching operating temperature
^
Incorrect ignition timing
^
Incorrect or clogged PCV system
^
Vacuum leaks (intake manifold, vacuum hoses, vacuum reservoirs, power brake booster etc.
VERIFY
^
Transmission is in PARK (A/T), or NEUTRAL (M/T)
^
Parking brake is applied (automatic brake disconnected where applicable)
^
Wheels blocked
^
Engine at operating temperature
^
Proper fuel pressure and no exhaust smoke
^
Correct and clean PCV system
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Heater, A/C, and other accessories OFF
^
Ignition timing is set to specification
^
EEC-IV diagnostics have been performed and vehicle malfunction indicated service output codes have been resolved.
STEP 1
With the engine OFF, connect a tachometer, according to manufacturer's instructions. Disconnect the negative (-) terminal of the battery for 5
minutes, then reconnect it.
STEP 2
START the engine and let stabilize for two minutes. Goose the accelerator and let the engine return to idle. Lightly depress and release the
accelerator, then let engine idle.
STEP 3
If the engine is not idling properly, turn the engine OFF, and disconnect Idle Speed Control Air Bypass Solenoid.
STEP 4
START and RUN the engine at 2500 rpm for 30 seconds.
STEP 5
Place the transmission is in PARK (A/T), or NEUTRAL (M/T).
STEP 6
Using a tachometer, verify idle rpm is 675 +50/-125 rpm.
RPM TOO LOW
a.
Turn the plate stop screw to reach an idle speed of 675 +/- 25 rpm.
NOTE: During engine break-in reduce the idle rpm by 100 rpm.
RPM TOO HIGH
a.
Turn the plate stop screw clockwise until 675 +/- 25 rpm is achieved.
STEP 7
Turn the engine OFF, and repeat Steps 4, 5, and 6, if necessary.
STEP 8
Run the KOEO Self-Test for proper TPS code output.
STEP 9
Turn the engine OFF, and disconnect the battery for at least 5 minutes.
STEP 10
Reconnect the Idle Speed Control Air Bypass Solenoid. Verify the throttle plate is not stuck in the bore, and the linkage is not preventing throttle
from closing.
STEP 11
START the engine and idle for two minutes. Goose the accelerator and let the engine return to idle. Lightly depress and release the accelerator,
then let engine idle.
^
If idle problem still exists, proceed to DIAGNOSIS AND TESTING PROCEDURES/TESTING PROCEDURES/QUICK TEST AND