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6-30 ENGINE GENERAL INFORMATION AND DIAGNOSIS
Condition
Improper engine
idling or engine fails
to idle
Excessive hydrocar-
bon (HC) emission
or carbon monox-
ide (CO)
Excessive nitrogen
oxides (NOx) emis-
sion
Possible Cause
Faulty spark plug
Leaky or disconnected high-tension cord
Faulty ignition coil with ignitor
Fuel pressure out of specification
Leaky manifold, throttle body, or cylinder
head gasket
Malfunctioning EGR valve (if equipped)
Faulty idle air control system
Faulty evaporative emission control system
Faulty EGR system (if equipped)
Faulty fuel injector(s)
Poor performance of ECT sensor, TP sensor
or MAP sensor
Faulty ECM
Loose connection or disconnection of vacuum
hoses
Malfunctioning PCV valve
Engine overheating
Low compression
Faulty spark plug
Leaky or disconnected high-tension cord
Faulty ignition coil with ignitor
Low compression
Lead contamination of three way catalytic
converter
Faulty evaporative emission control system
Fuel pressure out of specification
Closed loop system (A/F feed back compen-
sation) fails
• Faulty TP sensor
• Poor performance of ECT sensor or MAP
sensor
Faulty injector(s)
Faulty ECM
Engine not at normal operating temperature
Clogged air cleaner
Vacuum leaks
Improper ignition timing
Lead contamination of catalytic converter
Faulty EGR system (if equipped)
Fuel pressure out of specification
Closed loop system (A/F feed back compen-
sation) fails
• Faulty TP sensor
• Poor performance of ECT sensor or MAP
sensor
Faulty injector(s)
Faulty ECM
Correction
Spark plugs in Section 6F1.
High-tension cords in Section 6F1.
Ignition coil in Section 6F1.
Diagnostic Flow Table B-3.
EGR system in Section 6E1.
Diagnostic Flow Table B-4.
EVAP control system in Section 6E1.
EGR system in Section 6E1.
Diagnostic Flow Table B-1.
ECT sensor, TP sensor or MAP sensor
in Section 6E1.
PCV system in Section 6E1.
Refer to "Overheating" section.
Previously outlined.
Spark plugs in Section 6F1.
High-tension cords in Section 6F1.
Ignition coil assembly in Section 6F1.
Refer to "Low compression" section.
Check for absence of filler neck restric-
tor.
EVAP control system in Section 6E1.
Diagnostic Flow Table B-3.
TP sensor in Section 6E1.
ECT sensor or MAP sensor in Section
6E1.
Diagnostic Flow Table B-1
See section 6F1.
Check for absence of filler neck restric-
tor.
EGR system in Section 6E1.
Diagnostic Flow Table B-3.
TP sensor in Section 6E1.
ECT sensor or MAP sensor in Section
6E1.
Diagnostic Flow Table B-1
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