1991 LEXUS SC400 Throttle Position

INSPECTION OF VSV
1. DISCONNECT CABLE FROM NEGATIVE TERMINAL OFBATTERY
CAUTION: Work must be started after approx. 20 se-
conds or longer from the time the ignition switch is
turned to the ºLOCKº position and the negative (±) termi-
nal cable is disconnected from the battery.
2. REMOVE INTAKE AIR CONNECTOR (a) Disconnect the following hoses:(1) Air hose (from ISC valve) from intake air connector
(2) Air hose (from PS air control valve) from intake air
connector
(b) Remove the bolt holding the intake air connector to the cylinder head cover.
(c) Loosen the two hose clamps.
(d) Disconnect the intake air connector from the throttle
body and air cleaner hose, and remove the intake air
connector.
3. REMOVE VSV (a) Disconnect the VSV connector.
(b) Disconnect the following hoses:(1) Vacuum hose (from vacuum pipe) from VSV
(2) Vacuum hose (from charcoal canister) from VSV
(c) Remove the two bolts and VSV from the cylinder head.
(d) Disconnect the two wire clamps from the VSV bracket, and remove the VSV.
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EMISSION CONTROL SYSTEMS Fuel Evaporative Emission Control (EVAP) SystemEC±11
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EXHAUST GAS RECIRCULATION (EGR) SYSTEM
DESCRIPTION
To reduce NOx emission, part of the exhaust gases are recirculated through\
the EGR valve to the intake man-
ifold to lower the maximum combustion temperature.
OPERATION
To reduce NOx emission, part of the exhaust gases are recirculated through\
the EGR valve to the intake manifold to lower the
maximum combustion temperature.
Coolant
Temp.VSVThrottle Valve OpeningPressure in the EGR Valve Pressure ChamberEGR VacuumModulatorEGR
ValveExhaust Gas
Below 45
COPENCLOSEDNot recircu-
(113
F)OPEN±±±CLOSEDlated
Positioned be-
low EGR port±±CLOSEDNot recircula- ted
Above 50 5C
(122 5F)CLOSEDPositioned be-
tween EGRport
(1)
LOW* Pressure constantly
alternating between
OPENS passage to atmosphereCLOSEDNot recircula- ted
tween EGR port
and R port(2)
HIGHalternating between
low and highOPENS passage
to atmosphereOPENRecirculated
Above 50 5C
(122 5F)CLOSEDPositioned
above R port(3)
HIGH**CLOSES passage to atmosphereOPENRecirculated(increase)
* Pressure increases Modulator closes EGR valve opens Pressure drops EGR Valve closes Modulator opens
** When the throttle valve is positioned above the R port, the EGR vacuum m\
odulator will close the atmosphere passage and
open the EGR valve to increase the EGR gas, even if the exhaust pressure\
is insufficiently low.
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EMISSION CONTROL SYSTEMS Exhaust Gas Recirculation (EGR) SystemEC±11
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10. REMOVE RH NO.3 TIMING BELT COVERRemove the 3 bolts, timing belt cover and 3 gaskets.
11. DISCONNECT FUEL INLET HOSE FROM LH DELIVERY PIPE
Remove the pulsation damper and 2 gaskets, and discon-
nect the fuel inlet hose from the delivery pipe.
CAUTION:
w Put a shop towel under the delivery pipe.
w Slowly loosen the union bolt.
12. D I S C O N N E C T F U E L R E T U R N H O S E F R O M F U E L
RETURN PIPE
13. DISCONNECT PCV HOSE FROM LH CYLINDER HEAD
14. REMOVE LH NO.3 TIMING BELT COVER
(a) Remove the 4 bolts.
(b) Disconnect the cord grommet from the timing belt cover, and remove the timing belt cover and 3 gaskets.
(c) Remove the cord grommet from the high±tension cord.
15. DISCONNECT HEATER WATER VALVE FROM BODY
(a) Disconnect the VSV connector.
(b) Remove the bolt holding the engine wire clamp to the water valve bracket.
(c) Remove the 2 bolts, and disconnect the water valve and bracket assembly.
16. REMOVE THROTTLE BODY
(a) Disconnect the following connectors: (1) Throttle position sensor connector
(2) w/ TRAC:
Sub±throttle position sensor connector
(3) w/ TRAC:
Sub±throttle actuator connector
EG±16
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(e) Connect the following connectors:(1) Throttle position sensor connector
(2) w/ TRAC:Sub±throttle position sensor connector
(3) w/ TRAC: Sub±throttle actuator connector
27. REINSTALL HEATER WATER VALVE
(a) Install the water valve and bracket assembly with the 2 bolts.
(b) Install the engine wire clamp with the bolt.
(c) Connect the VSV connector.
28. REINSTALL RH NO.3 TIMING BELT COVER
(a) Install the 3 gaskets to the timing belt cover.
(b) Fit the portion A of the timing belt cover, matching it with the lower high±tension cord cover.
(c) Install the timing belt cover with the 3 bolts.
29. REINSTALL VSV FOR EVAP SYSTEM Install the VSV with the 2 bolts.
30. REINSTALL LH NO.3 TIMING BELT COVER
(a) Install the 3 gaskets to the timing belt cover.
(b) Install the cord grommet to the high±tension cord (from the LH ignition coil).
(c) Install the cord grommet to the timing belt cover.
(d) Fit the portion A of the timing belt cover, matching it with the lower high±tension cord cover.
(e) Install the timing belt cover with the 4 bolts.
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1UZ±FE ENGINE ENGINE MECHANICALEG±29
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(b) Connect the tester probe of a timing light to the high ±tension
cord for No.6 cylinder.
(c) Using a timing light, check the ignition timing.
Ignition timing: 8 ± 12 5 BTDC @ idle
(Transmission in neutral position)
If the ignition timing is not as specified, check that following
conditions are normal:
w Throttle valve fully closed
w Continuity between terminals IDL1 and E2 of the throttle
position sensor
w Valve timing
(d) Remove the SST from the DLC1. SST 09843±18020
5. DISCONNECT TACHOMETER AND TIMING LIGHT FROM ENGINE
6. REINSTALL UPPER HIGH±TENSION CORD COVER
(a) Fit portion A of the upper high±tension cord cover matching the top of the lower high±tension cord cover.
(b) Push the front side of the upper high±tension cord cover, and
fit the front side claw groove of the upper high±tension cord
cover to the claw of the lower high ±tension cord cover.
(c) Install the upper high±tension cord cover with the 2 bolts.
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1UZ±FE ENGINE ENGINE MECHANICALEG±33
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Troubleshooting
If the CO/HC concentration does not comply with regulations,
perform troubleshooting in the order given below.
(a) Check main heated oxygen sensor operation.
(See MFI System on page EG±400)
(b) See the table below for possible causes, and then inspect and correct the applicable causes if necessary.
 CO HC Problems\
 \
Causes
 Normal High Rough idle\
 \
1. Faulty ignitions: 


 


 


\
 

\

Incorrect timing
   \
 \
Fouled, shorted or improperly gapped plugs
   \
 \
Open or crossed high±tension cords
   \
 \
Cracked distributor cap
   \
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2. Incorrect valve clearance   \
 \
3. Leaky EGR valve 


 


 


\
 

\
4. Leaky intake and exhaust valves
   \
 \
5. Leaky cylinder
 Low High Rough idle\
 \
1. Vacuum leaks:
   (Fluctuating HC reading)\
 \

PCV hose
   \
 \
EGR valve 


 


 


\
 

\

Intake manifold
   \
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Throttle body
   \
 \
IAC valve
   \
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Brake booster line
   \
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2. Lean mixture causing misfire 

High 

High 

Rough idle\
 

\
1. Restricted air filter
   (Black smoke from exhaust)\
 \
2. Faulty MFI systems:
   \
 \

Faulty pressure regulator
   \
 \
Clogged fuel return line
   \
 \
Defective ECT switch   \
 \
Faulty ECM 


 


 


\
 

\

Faulty injector
   \
 \
Faulty throttle position sensor
   \
 \
Faulty volume air flow meter
V02130
EG±36±
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15. CHECK CYLINDER COMPRESSION PRESSURE
(a) Reconnect the battery negative (±) cable.
(b) Insert a compression gauge into the spark plug hole.
(c) Fully open the throttle.
(d) Wh ile cra n kin g th e en g in e , me a su re th e co mp re ssio npressure.
HINT: Always use a fully charged battery to obtain engine
speed of 250 rpm or more.
(e) Repeat steps (b) through (d) for each cylinder. NOTICE: This measurement must be done in as short a
time as possible.
Compression pressure:
1,226 kPa (12.5 kgf/cm
2, 178 psi) or more
Minimum pressure: 981 kPa (10.0 kgf/cm
2, 142 psi)
Difference between each cylinder: 98 kPa (1.0 kgf/cm
2, 14 psi) or less
(f) If the cylinder compression in one or more cylinders is low,pour a sm all amount of engine oil into the cylinder through the
spark plug hole and repeat steps (b) through (d) for cylinders
with low compression.
w If adding oil helps the compression, it is likely that the
piston rings and/or cylinder bore are worn or damage.
w If pressure stays low, a valve may be sticking or seating
is improper, or there may be leakage past the gasket.
(g) Disconnect the battery negative (±) cable.
16. REINSTALL SPARK PLUGS
Using a 16 mm plug wrench, install the 8 spark plugs.
Torque: 18 N Vm (180 kgf Vcm, 13 ft Vlbf)
17. R E C O N N E C T H I G H ± T E N S I O N C O R D S TO S PA R K
PLUGS
18. RECONNECT RH CAMSHAFT POSITION SENSOR CONNECTOR
(a) Connect the camshaft position sensor connector.
(b) Install the camshaft position sensor connector to the ignition
coil bracket.
EG±40
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24. REINSTALL RH ENGINE WIRE COVER
(a) Fit portions A and B of the engine wire cover, matching themwith the lower high±tension cord cover and No.3 timing belt
cover.
(b) Install the timing belt cover with the bolt.
25. REINSTALL LH ENGINE WIRE COVER
(a) Connect portions A and B of the engine wire cover to the wire
brackets.
(b) Set the VSV (for the fuel pressure) wire in original position.
(c) Fit portions C and D of the engine wire cover, matching them with the lower high±tension cord cover and No.3 timing belt
cover.
(d) Install the timing belt cover with the 2 bolts.
26. REINSTALL UPPER HIGH±TENSION CORD COVER
(a) Fit portion A of the upper high±tension cord cover matching the top of the lower high±tension cord cover.
(b) Push the front side of the upper high±tension cord cover, and
fit the front side claw groove of the upper high±tension cord
cover to the claw of the lower high ±tension cord cover.
(c) Install the upper high±tension cord cover with the 2 bolts.
27. REINSTALL INTAKE AIR CONNECTOR
(a) Connect the end portions of the intake air connector to the throttle body and air cleaner hose.
(b) Tighten the 2 hose clamps.
(c) Install the bolt holding the intake air connector to the cylinder head cover.
EG±42
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