Engine hesitates
(Momentary lack of
response as the
accelerator is depressed.
Can occur at all vehicle
speeds. Usually most
severe when first trying to
make the vehicle move, as
from a stop sign.)

Spark plug faulty or plug gap as out of
adjustment

Refer to “Spark Plug Inspection in Section 1H”.

Fuel pressure out of specification
– Dirty fuel filter
– Dirty or clogged fuel hose or pipe
– Faulty fuel pressure regulator
– Faulty fuel pump

Refer to “Fuel Pressure Check”.

Engine overheating

Refer to condition of “Overheating”.

Faulty EGR system (if equipped)

Refer to “EGR System Inspection (If Equipped)
in Section 1B”.

Faulty injector

Refer to “Fuel Injector Inspection in Section
1G”.

Faulty ECT sensor or MAF sensor

Refer to “Engine Coolant Temperature (ECT)
Sensor Inspection in Section 1C” or “Mass Air
Flow (MAF) and Intake Air Temperature (IAT)
Sensor On-Vehicle Inspection in Section 1C”.

Faulty ECM

Refer to “Inspection of ECM and Its Circuits”.

Low compression

Refer to “Compression Check in Section 1D”.

Faulty electric throttle body assembly

Refer to “Electric Throttle Body Assembly On-
Vehicle Inspection in Section 1C”.

Faulty accelerator pedal position (APP)
sensor assembly

Refer to “Accelerator Pedal Position (APP)
Sensor Assembly Inspection in Section 1C”.

Condition

Possible cause

Correction / Reference Item

Engine General Information and Diagnosis: 1A-54

Surges
(Engine power variation
under steady throttle or
cruise. Feels like the
vehicle speeds up and
down with no change in
the accelerator pedal.)

Defective spark plug (excess carbon
deposits, improper gap, and burned
electrodes, etc.)

Refer to “Spark Plug Inspection in Section 1H”.

Variable fuel pressure
– Dirty fuel filter
– Dirty or clogged fuel hose or pipe
– Faulty fuel pressure regulator
– Faulty fuel pump

Refer to“Fuel Pressure Check”.

Faulty EGR system (if equipped)

Refer to “EGR System Inspection (If Equipped)
in Section 1B”.

Faulty MAF sensor

Refer to “Mass Air Flow (MAF) and Intake Air
Temperature (IAT) Sensor On-Vehicle
Inspection in Section 1C”.

Faulty injector

Refer to “Fuel Injector Inspection in Section
1G”.

Faulty ECM

Refer to “Inspection of ECM and Its Circuits”.

Faulty electric throttle body assembly

Refer to “Electric Throttle Body Assembly On-
Vehicle Inspection in Section 1C”.

Faulty accelerator pedal position (APP)
sensor assembly

Refer to “Accelerator Pedal Position (APP)
Sensor Assembly Inspection in Section 1C”.

Excessive detonation
(The engine makes sharp
metallic knocks that
change with throttle
opening. Sounds like pop
corn popping.)

Engine overheating

Refer to condition of “Overheating”.

Faulty spark plug

Refer to “Spark Plug Inspection in Section 1H”.

Improper ignition timing

Refer to “Ignition Timing Inspection in Section
1H”.

Clogged fuel filter and fuel lines

Refer to “Fuel Pressure Check”.

Faulty EGR system (if equipped)

Refer to “EGR System Inspection (If Equipped)
in Section 1B”.

Faulty knock sensor, ECT sensor or
MAF sensor

Refer to “DTC P0327 / P0328: Knock Sensor
Circuit Low / High”, “Engine Coolant
Temperature (ECT) Sensor Inspection in
Section 1C” or “Mass Air Flow (MAF) and
Intake Air Temperature (IAT) Sensor On-
Vehicle Inspection in Section 1C”.

Faulty injector

Refer to “Fuel Injector Inspection in Section
1G”.

Faulty ECM

Refer to “Inspection of ECM and Its Circuits”.

Excessive combustion chamber
deposits

Refer to “Cylinder Head Inspection in Section
1D” and “Cylinders, Pistons and Piston Rings
Inspection in Section 1D”.

Fuel pressure out of specification
– Dirty fuel filter
– Dirty or clogged fuel hose or pipe
– Faulty fuel pressure regulator
– Faulty fuel pump

Refer to “Fuel Pressure Check”.

Air drawn in through intake manifold or
throttle body gasket

Check air intake system.

Condition

Possible cause

Correction / Reference Item

1A-55 Engine General Information and Diagnosis:

Overheating

Inoperative thermostat

Refer to “Thermostat Inspection in Section 1F”.

Poor water pump performance

Refer to “Water Pump Inspection in Section
1F”.

Clogged or leaky radiator

Refer to “Radiator On-Vehicle Inspection and
Cleaning in Section 1F”.

Improper engine oil grade

Refer to “Engine Oil and Filter Change in
Section 0B”.

Clogged oil filter or oil strainer

Refer to “Engine Oil and Filter Change in
Section 0B” or “Oil Pan and Oil Pump Strainer
Cleaning in Section 1E”.

Poor oil pump performance

Refer to “Oil Pump Inspection in Section 1E”.

Dragging brakes

Refer to condition: “Dragging brakes” in
“Brakes Symptom Diagnosis in Section 4A”.

Slipping clutch

Refer to condition: “Slipping clutch” in “Clutch
(Hydraulic Type) Symptom Diagnosis in
Section 5C”.

Blown cylinder head gasket

Refer to “Cylinder Head Inspection in Section
1D”.

Faulty radiator cooling fan control
system

Refer to “DTC P0480 / P0481 / P0482: Fan 1 /
Fan 2 / Fan 3 Control Circuit”.

Air mixed in cooling system

Release air from cooling system.

Poor gasoline mileage

Faulty spark plug (improper gap, heavy
deposits, and burned electrodes, etc.)

Refer to “Spark Plug Inspection in Section 1H”.

Fuel pressure out of specification

Refer to “Fuel Pressure Check”.

Faulty ECT sensor or MAF sensor

Refer to “Engine Coolant Temperature (ECT)
Sensor Inspection in Section 1C” or “Mass Air
Flow (MAF) and Intake Air Temperature (IAT)
Sensor On-Vehicle Inspection in Section 1C”.

Faulty EGR system (if equipped)

Refer to “EGR System Inspection (If Equipped)
in Section 1B”.

Faulty injector

Refer to “Fuel Injector Inspection in Section
1G”.

Faulty ECM

Refer to “Inspection of ECM and Its Circuits”.

Low compression

Refer to “Compression Check in Section 1D”.

Poor valve seating

Refer to “Valves and Valve Guides Inspection
in Section 1D”.

Dragging brakes

Refer to condition: “Dragging brakes” in
“Brakes Symptom Diagnosis in Section 4A”.

Slipping clutch

Refer to condition: “Slipping clutch” in “Clutch
(Hydraulic Type) Symptom Diagnosis in
Section 5C”.

Thermostat out of order

Refer to “Thermostat Inspection in Section 1F”.

Improper tire pressure

Adjust tire pressure.

High idle speed

Refer to “Improper engine idling or engine fails
to idle” under “Engine Symptom Diagnosis”.

Faulty electric throttle body assembly

Refer to “Electric Throttle Body Assembly On-
Vehicle Inspection in Section 1C”.

Faulty accelerator pedal position (APP)
sensor assembly

Refer to “Accelerator Pedal Position (APP)
Sensor Assembly Inspection in Section 1C”.

Condition

Possible cause

Correction / Reference Item

Engine General Information and Diagnosis: 1A-56

Excessive engine oil
consumption

Sticky piston ring

Refer to “Cylinders, Pistons and Piston Rings
Inspection in Section 1D”.

Worn piston and cylinder

Refer to “Cylinders, Pistons and Piston Rings
Inspection in Section 1D”.

Worn piston ring groove and ring

Refer to “Cylinders, Pistons and Piston Rings
Inspection in Section 1D”.

Improper location of piston ring gap

Refer to “Pistons, Piston Rings, Connecting
Rods and Cylinders Disassembly and
Reassembly in Section 1D”.

Worn or damaged valve stem seal

Replace.

Worn valve stem

Refer to “Valves and Valve Guides Inspection
in Section 1D”.

Low oil pressure

Improper oil viscosity

Refer to “Engine Oil and Filter Change in
Section 0B”.

Malfunctioning oil pressure switch

Refer to “Oil Pressure Switch Inspection in
Section 9C”.

Clogged oil strainer

Refer to “Oil Pan and Oil Pump Strainer
Cleaning in Section 1E”.

Functional deterioration of oil pump

Refer to “Oil Pump Inspection in Section 1E”.

Worn oil pump relief valve

Refer to “Oil Pump Inspection in Section 1E”.

Excessive clearance in various sliding
parts

Engine noise

NOTE
Before checking the
mechanical noise, make
sure that:
• Ignition timing.
• Specified spark plug is

used.

• Specified fuel is used.

Improper valve lash

Refer to “Valve Lash (Clearance) Inspection in
Section 1D”.

Worn valve stem and guide

Refer to “Valves and Valve Guides Inspection
in Section 1D”.

Weak or broken valve spring

Refer to “Valve Springs Inspection in Section
1D”.

Warped or bent valve

Refer to “Valves and Valve Guides Inspection
in Section 1D”.

Loose camshaft housing bolts

Refer to “Camshafts, Tappets and Shims
Removal and Installation in Section 1D”.

Worn piston, ring and cylinder bore

Refer to “Cylinders, Pistons and Piston Rings
Inspection in Section 1D”.

Worn crank pin bearing

Refer to “Crank Pins and Connecting Rod
Bearings Inspection in Section 1D”.

Worn crank pin or connecting rod
bearings

Refer to “Crank Pins and Connecting Rod
Bearings Inspection in Section 1D”.

Loose connecting rod nuts

Refer to “Pistons, Piston Rings, Connecting
Rods and Cylinders Removal and Installation
in Section 1D”.

Low oil pressure

Refer to condition “Low oil pressure” previously
described.

Worn crankshaft journal bearing

Refer to “Main Bearings Inspection in Section
1D”.

Worn crankshaft journal

Refer to “Crankshaft Inspection in Section 1D”.

Loose lower crankcase (bearing cap)
bolts

Refer to “Main Bearings, Crankshaft and
Cylinder Block Removal and Installation in
Section 1D”.

Excessive crankshaft thrust play

Refer to “Crankshaft Inspection in Section 1D”.

Condition

Possible cause

Correction / Reference Item

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