C 3500 Truck 2WD V8-305 5.0L (1986)
Idle Speed Control Motor: Adjustments
On engines equipped with an idle speed control motor, idle speed is controlled by an electrical signal from the ECM. Do not use the ISC plunger to
adjust 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 Underhood Emission Label.
Plunger - Maximum Adjustment
NOTE: Prior to adjustment, check for an identification letter on the ISC plunger. If NO LETTER appears, using Tool J-29607, BT-8022 or equivalent,
remove plunger from ISC Unit. Then, measure length of plunger from back side of plunger head to end of plunger screw - Dimension "A".
Record this measurement for use at Step 17. Reinstall plunger in ISC unit, turning plunger into a preset position so that the distance measured
from the back side of the plunger head to the ISC nosepiece is LESS THAN Dimension "B".
ISC PLUNGER ADJUSTMENT CHART
Identification
Plunger Length
Plunger Length
Letter
Dimension "A"
Dimension "B"
None
14.1 mm (9/16")
5.6 mm (7/32")
None
16.3 mm (41/64")
8.0 mm (5/16")
X
18.5 mm (47/64")
10.0 mm (25/6'4")
A
19.3 mm (49/64")
10.8 mm (27/64")
Y
20.5 mm (51/64")
12.0 mm (15/32")
S
21.2 mm (27/32")
12.7 mm (1/2")
Z
22.5 mm (7/8")
14.0 mm (35/64")
G
23.2 mm (29/32")
14.7 mm (37/64")
E
25.6 mm (1LL)
17.1 mm (43/64")
L
27.5 mm (1 -3/32")
19.0 mm (3/4")
J
30.0 mm (1-3/16")
21.5 mm (27/32")
N
32.0 mm (1-17/64")
23.5 mm (59/64")
T
34.0 mm (1-11/32")
25.5 mm (1")