GMC G Service Manual page 552

6A-20 ENGINE. DRIVEABILITY AND DIAGNOSIS
DIAGNOSIS OF STARTING/IDLING/SHUTOFF
PROBLEM
Engine Diesels (After
Run) Upon Shut Off
PROBLEMS (CONT.)
POSSIBLE CAUSE
1. Minimum (base) idle speed misadjusted.
2. (1MEF)
Idle stop solenoid malfunctioning. Faulty sole­
noid circuit wiring.
(M4MEF)
Idle stop solenoid or throttle kicker
malfunctioning.
Faulty solenoid circuit wiring.
3. Choke not operating properly or fast idle cam
sticking or binding.
4. Throttle linkage or throttle shaft sticking or
binding.
5. (1MEF)
Air leaks at carburetor flange/insulator gas-
ket(s), or at intake manifold gasket. Vacuum
hoses disconnected or improperly installed.
(M4MEF)
Air leaks at carburetor flange gasket(s), or at
intake manifold gasket(s). Vacuum hoses dis­
connected or improperly installed.
6. PCV system malfunctioning.
7. Ignition timing retarded (causes throttle valve
to be opened farther than normal to obtain
correct idle speed).
8. Lean idle mixture (causes throttle valve to be
opened farther than normal to obtain correct
idle speed).
CORRECTION
1. Adjust minimum (base) idle speed. See Emis­
sion Control Information Label on vehicle.
2. (1MEF)
See "Checking Idle Stop Solenoid (ISS)" in
CARBURETORS (SEC. 6C1).
(M4MEF)
See "Checking Idle Stop Solenoid (ISS)" in
CARBURETORS (SEC. 6C1). Also refer to
"Diagnosis of TRC" in CARBURETOR EMIS­
SIONS (SEC. 6E1).
3. Check choke valve and fast idle cam for free
movement. Check for complete opening and
closing of choke valve. See "Choke Checking
Procedure (Engine Off)" and "Checking Elec­
tric Choke" in CARBURETORS (SEC. 6C1).
4. Check throttle linkage and throttle shaft(s) for
smooth and free operation. Clean with suitable
solvent. Replace throttle body if necessary.
5. Use pressure oil can to spray light oil or ker­
osene around carburetor throttle body (do not
spray at throttle shaft ends), and manifold to
head mounting surfaces.
If engine RPM changes, torque carburetor
to manifold bolts and/or intake manifold bolts
to specification. If necessary, replace the car­
buretor flange/insulator gasket(s) and/or in­
take manifold gasket(s). Check condition and
routing of vacuum hoses. Correct or replace
as necessary. Refer to Emission Control Infor­
mation Label for correct routing.
6. Check PCV system. Clean or replace PCV
valves and hoses as necessary.
7. Adjust timing. See Emission Control Informa­
tion Label.
8. Clean carburetor if necessary. Adjust idle mix­
ture per specified procedure.
GMTB-0919-2L