HOT (SLOW) IDLE RPM ADJUSTMENT
Idle Speed Control Motor
Idle speed is controlled by the Idle Speed Control (ISC) motor, which in turn is controlled by an
electrical signal from the ECM. DO NOT adjust the ISC plunger to adjust the curb idle. The motor
varies idle speed from a base (minimum authority) to a high (maximum authority) idle speed. DO NOT
adjust unless diagnosis indicates a malfunction. Check for proper base and high idle speed as follows.
See the MINIMUM & MAXIMUM AUTHORITY IDLE RPM table for the correct idle speed
1. Prior to making adjustments, check for an identification letter on ISC plunger. See Fig. 4 . If no
letter appears, remove plunger and measure length of plunger (distance "A" in Fig. Fig. 4 ).
Record measurement. Install plunger into ISC and position so that distance measured from back
side of plunger to ISC is less than distance "B" listed in IDLE SPEED CONTROL PLUNGER
2. Place transmission in "P". Set brakes and block wheels. Connect tachometer to engine. Connect
dwell meter to Mixture Control Solenoid dwell lead. Set dwell meter to 6-cylinder scale. Turn
A/C off (if equipped), start engine and run until stabilized and in "Closed Loop" operation (dwell
meter needle starts to fluctuate). Turn ignition OFF.
3. Unplug ISC connector from motor. Retract plunger by applying 12 volts to terminal "C" and
grounding terminal "D" of ISC motor. See Fig. 5 .
4. Start engine and run until dwell meter starts to vary (Closed Loop operation), then place
transmission in DRIVE. Adjust carburetor (slow) idle stop screw to Minimum Authority RPM,
see the MINIMUM & MAXIMUM AUTHORITY IDLE RPM table for the proper
specifications. With idle adjusted, place transmission in PARK.
5. Extend ISC plunger by applying 12 volts to terminal "D" and grounding terminal "C" of ISC
motor connector. See Fig. 5 . Place transmission in DRIVE (preset the ISC plunger to obtain 1500
RPM, before placing it in DRIVE) and adjust the ISC plunger to Maximum Authority RPM.
Recheck Maximum RPM adjustment by applying voltage to extend the plunger (plunger will
ratchet at full extension).
CAUTION: DO NOT disconnect or connect ISC connector with ignition ON
or damage to the ECM may result.
CAUTION: DO NOT leave 12 volts connected to the ISC motor any longer
than is absolutely necessary to retract the plunger. Prolonged
contact will result in damage to the motor.
CAUTION: NEVER connect a voltage source across terminals "A" and "B"
or Nose Switch (internal throttle contact switch) will be
NOTE: When the plunger is in the fully extended position, the plunger must
be in contact with the throttle lever to prevent possible internal
TUNE-UP - 3.8L V6 VIN [A] -1984 Buick Regal Page 1 of 2
6. After adjustment, measure distance from back of plunger head to ISC motor (distance "B" in Fig.
Fig. 4 ). Distance must NOT exceed distance listed in IDLE SPEED CONTROL PLUNGER
7. Fully retract plunger and turn engine OFF. Disconnect all test equipment and wires. Be sure
ignition is OFF, then reconnect ISC motor 4-terminal connector. Clear diagnostic trouble code by
removing ECM fuse from fuse block for about 10 seconds.
Fig. 4: Measuring Idle Speed Control Plunger
Fig. 5: Idle Speed Control Adjustment Connections
IDLE SPEED CONTROL PLUNGER SETTING
MINIMUM & MAXIMUM AUTHORITY IDLE RPM (1)
damage to unit.
Identification Distance "A" In. (mm) Distance "B" In. (mm)
None 9/16" (14.1) 7/32" (5.6)
None 41/64" (16.3) 5/16" (8.0)
X 47/64" (18.5) 25/64" (10.0)
A 49/64" (19.3) 27/64" (10.8)
Y 51/64" (20.5) 15/32" (12.0)
S 27/32" (21.2) 1/2" (12.7)
Z 7/8" (22.5) 35/64" (14.0)
G 29/32" (23.2) 37/64" (14.7)
E 1" (25.6) 43/64" (17.1)
L 1 3/32" (27.5) 3/4" (19.0)
J 1 3/16" (30.0) 27/32" (21.5)
N 1 17/64" (32.0) 59/64" (23.5)
T 1 11/32" (34.0) 1" (25.5)
Application Minimum Authority Maximum Authority
3.8L 2-Bbl. (VIN A) A/T 450 (2) 1000 (3)
(1) Auto. Trans. RPM given for vehicle in DRIVE.
(2) Plus or minus 25 RPM
(3) Plus or minus 100 RPM
TUNE-UP - 3.8L V6 VIN [A] -1984 Buick Regal Page 2 of 2
Monday, April 13th, 2009 AT 4:34 PM