Toyota 4A-FE Repair Manual page 22

EM-24
ENGINE MECHANICAL - Engine Tune-up (4A-FE)
If the CO concentration is not as specified, adjust the idle
mixture by turning the IDLE MIXTURE ADJUSTING
SCREW in the variable resistor.
• If the concentration is within specification, this adjust-
ment is complete.
• 1f the CO concentration cannot be corrected by idle
mixture adjustment, see the table below for other possi-
ble causes.
HINT:
Always check the idle speed after turning the idle
F1601s
mixture adjusting screw. If it is incorrect, repeat steps 5
L--~~~~~~~~~~~~~~~-'
and 6.
FIS081
Troubleshooting
HC
co
SYMPTOMS
CAUSES
High Normal Rough idle 1. Faulty ignition:
• Incorrect timing
• Fouled, shorted or improperly gapped plugs
• Open or crossed ignition wires
• Cracked llA cap
2. Incorrect valve clearance
3. Leaky
EGA
valve (w/ EGR system)
4. Leakt intake and exhaust valves
5. Leaky cylinder
High Low
I
Rough idle 1. Vacuum leak:
• Vacuum hose
(Fluctuating HC reading)
• EGR
valve {w/ EGR system)
I
• Intake manifold
•
PCV line
•
Throttle body
I
•
Cylinder head gasket
• Brake booster line
2. Lean mixture causing misfire
High High Rough idle 1 . Restricted air filter
2. Plugged PCV valve
3. Faulty EFI system
(Black smoke from exhaust)
•
Faulty pressure regulator
•
Clogged fuel return line
•
Faulty vacuum sensor
•
Defective water temp. sensor
•
Defective intake air temp. sensor
• Faulty ECU
•
Faulty injector
•
Faulty cold start injector
• Faulty throttle position sensor