1991 LEXUS SC400 sensor

(b) Install a new gasket and throttle body with the two boltsand two nuts.
Torque: 18 N Vm (185 kgf Vcm, 13 ft Vlbf)
HINT: Use bolts 40 mm (1.57 in.) in length.
(c) Install the water by±pass pipe (from rear water by±pass
joint) to the clamp on the engine wire cover.
(d) Connect the following hoses: (1) Water by±pass hose to the ISC valve
(2) (USA Spec.) Vacuum hose to throttle body
(3) (Exc. USA Spec.) Three vacuum hoses to throttle body
(e) Connect the following connectors: (1) Throttle position sensor connector
(2) (w/ TRAC) Sub±throttle position sensor connector
(3) (w/ TRAC) Sub±throttle actuator
27. REINSTALL HEATER WATER VALVE (a) Install the water valve and bracket assembly with thetwo bolts.
(b) Install the engine wire clamp with the bolt.
(c) Connect the VSV connector.
EM±24
±
ENGINE MECHANICAL Engine Tune±Up
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Troubleshooting
If the CO/HC readings do not comply with regulations, pre-
form troubleshooting in the order given below.
(a) Check oxygen sensor operation.(See page FI±73)
(b) See the table below for possible cause, and then inspect
and correct the applicable causes if necessary.
 CO HC Symptoms Cause
 Normal High Rough idle 1. Faulty ignition:
     Incorrect timing
     Fouled, shorted or improperly gapped plugs
 Open or crossed high±tension cords     Cracked distributor cap    2. Incorrect valve clearance    3. Leaky EGR valve    4. Leaky intake and exhaust valves
    5. Leaky cylinder
 Low High Rough idle 1. Vacuum leak:
   (Fluctuating HC reading)  PCV hose
     EGR valve
     Intake manifold
     Air intake chamber
 Throttle body     ISC valve     Brake booster line    2 Lean mixture causing misfire High High Rough idle 1. Clogged air filter
   (Black smoke from exhaust) 2. Faulty EFI system
     Faulty pressure regulator
     Clogged fuel return line
     Defective engine coolant temp. sensor
     Defective intake air temp. sensor
     Faulty ECU
 Fault injectors     Faulty throttle position sensor     Faulty volume air flow meter
±
ENGINE MECHANICAL Idle and/or 2,500 rpm CO/HC CheckEM±21
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Troubleshooting
If the HC/CO concentration does not comply with regulations,
perform troubleshooting in the order given below.
(a) Check oxygen sensor operation.(See page FI±113)
(b) See the table below for possible cause, and then inspect
and correct the applicable causes if necessary.
 

HC 

CO 

Symptoms\
 

\
Cause
 High Normal Rough idle\
 \
1. Faulty ignitions:
   \
 \

Incorrect timing
   \
 \

Fouled, shorted or improperly gapped plugs
   \
 \

Open or crossed high±tension cords
Ckddiib\

Cracked distributor cap
Ill   \
 \
2. Incorrect valve clearance
3 L k EGR l   \
 \
3. Leaky EGR valve
4L k i k d h l   \
 \
4. Leaky intake and exhaust valves
L k li d   \
 \
5. Leaky cylinders
 High Low Rough idle\
 \
1. Vacuum leaks:
   (Fluctuating HC reading)\
 \

PCV hoses
   \
 \

EGR valve
   \
 \

Intake manifold
Ai i k h b   \
 \

Air intake chamber
Th l b d   \
 \

Throttle body
ISC l\

ISC valve
Bkb li   \
 \

Brake booster line
2L i i ifi   \
 \
2. Lean mixture causing misfire
 High High Rough idle\
 \
1. Clogged air filter g g g
(Black smoke from exhaust)\
 \
gg
2. Faulty EFI systems:   ()\
 \
yy

Faulty pressure regulator
   \
 \

yg

Clogged fuel return line
   \
 \

gg

Defective water temp. sensor
   \
 \

Defective air temp. sensor
   \
 \

Faulty ECU
   \
 \

y

Faulty injectors
\

yj

Faulty cold start injector   \
 \
yj

Faulty throttle position sensor   \
 \

Faulty air flow meter
±
ENGINE MECHANICAL Idle and/or 2,500 rpm HC/CO
Concentration Check MethodEM±29
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COMPRESSION CHECK
HINT: If there is lack of power, excessive oil consumption or
poor fuel economy, measure the compression pressure.
1. WARM UP AND STOP ENGINE Allow the engine to warm up to normal operating tempera-
ture.
2. REMOVE NO.3 TIMING BELT COVERS (See steps 1, 5 to 10 and 14 on pages EM±11 to 13)
3. DISCONNECT COLD START INJECTOR CONNECTOR
4. DISCONNECT RH CAM POSITION SENSOR CONNECTOR
(a) Disconnect the connector from the ignition coil bracket.
(b) Disconnect the sensor connector.
5. DISCONNECT LH CAM POSITION SENSOR CONNECTOR
6. REMOVE SPARK PLUGS (a) Disconnect the eight high±tension cords from the sparkplugs.
Disconnect the high±tension cords at rubber boot. Do
not pull on the cords.
NOTICE: Pulling on or bending the cords may damage
the conductor inside.
EM±30
±
ENGINE MECHANICAL Compression Check
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9. RECONNECT RH CAM POSITION SENSOR CONNECTOR
(a) Connect the sensor connector.
(b) Connect the connector to the ignition coil bracket.
10. RECONNECT LH CAM POSITION SENSOR CONNECTOR
11. RECONNECT COLD START INJECTOR CONNECTOR
12. REINSTALL NO.3 TIMING BELT COVERS (See steps 28 to 30, 34 to 37, 40 and 41 on pages EM±25
to 27)
EM±32
±
ENGINE MECHANICAL Compression Check
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15. REMOVE HIGH±TENSION CORDS, HIGH±TENSIONCORD CLAMPS AND LOWER HIGH±TENSION CORD
COVER ASSEMBLY
(a) Remove the two bolts holding the RH rear high±tensioncord clamp to the cylinder head.
(b) Disconnect the high±tension cords from the RH spark plugs and distributor cap.
(c) Remove the two bolts holding the LH rear high±tension cord clamp to the cylinder head.
(d) Disconnect the high±tension cords from the LH spark
plugs, distributor cap and LH ignition coil.
(e) Remove the bolt holding the lower high±tension cord cover to the water inlet housing.
(f) Disconnect the high±tension cord from the RH ignition
coil, and remove the high±tension cords, clamps and
cover assembly.
16. REMOVE DRIVE BELT IDLER PULLEY Remove the pulley bolt, cover plate and idler pulley.
17. REMOVE RH NO.2 TIMING BELT COVER (a) Disconnect the cam position sensor connector from theignition coil bracket.
EM±38
±
ENGINE MECHANICAL Timing Belt
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(b) Disconnect the cam position sensor wire from the clamp
on the timing belt cover.
(c) Remove the five mounting bolts.
(d) Disconnect the connector grommet from the timing belt cover.
(e) Disconnect the wire clamp from the timing belt cover, and remove the timing belt cover and four gaskets.
18. REMOVE LH NO.2 TIMING BELT COVER (a) Disconnect the cam position sensor wire from the clamp
on the timing belt cover.
(b) Disconnect the cam position sensor connector.
(c) Remove the three mounting bolts.
(d) Disconnect the connector grommet from the timing belt cover, and remove the timing belt cover and two
gaskets.
19. REMOVE DISTRIBUTOR CAPS Loosen the three bolts, and remove the distributor cap. Re-
move the two distributor caps.
HINT: Arrange the distributor caps (RH side and LH side).
20. REMOVE DISTRIBUTOR ROTORS Loosen the two bolts, and remove the distributor rotor.
Remove the two distributor rotors.
HINT: Arrange the distributor rotors (RH side and LH side).
21. REMOVE DISTRIBUTOR HOUSINGS (a) (RH Distributor Housing)Disconnect the cam position sensor connector.
(b) Re mo ve th e th re e bo lts an d distrib u to r ho u sin g . Remove the two distributor housings.
±
ENGINE MECHANICAL Timing BeltEM±39
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(a) Disconnect the solenoid valve connector.
(b) Remove the two mounting bolts and two mounting nuts.
(c) Disconnect the engine speed sensor wire clamp.
(d) Remove the hydraulic pump.
32. REMOVE NO.1 TIMING BELT COVER Remove the four bolts, timing belt cover and gasket.
33. REMOVE TIMING BELT COVER SPACER Remove the cover spacer and gasket.
34. REMOVE TIMING BELT GUIDE (NO.1 CRANK ANGLE SENSOR PLATE)
35. REMOVE TIMING BELT HINT (Re±using timing belt): If the installation marks have
disappeared, place a new installation mark on the timing belt
to match the dot mark of the crankshaft timing pulley.
±
ENGINE MECHANICAL Timing BeltEM±43
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