Lexus SC300 / Lexus SC400. Manual — part 422

IDLE AND/OR 2,500 RPM CO/HC
CHECK

HINT: This check is used only to determine whether or not the
idle CO/HC complies with regulations.

1. INITIAL

CONDITIONS

(a) Engine at normal operating temperature.
(b) Air cleaner installed.
(c) All pipes and hoses of air induction system connected.
(d) All accessories switched OFF.
(e) All vacuum lines properly connected.
HINT: All vacuum hoses for EGR systems, etc. should be
properly connected.
(f) SFI system wiring connectors fully plugged.
(g) Transmission in neutral.
(h) Tachometer and CO/HC analyzer calibrated and at

hand.

2. START

ENGINE

3. RACE ENGINE AT 2,500 RPM FOR APPROX. 120

SECONDS

4. INSERT

CO/HC

ANALYZER

TESTING

PROBE

INTO

TAILPIPE AT LEAST 40 cm (1.3 ft)

CHECK CO/HC CONCENTRATION AT IDLE AND/OR
2,500 RPM
Complete the measuring within three minutes.
HINT: When performing the two mode (2,500 rpm and idle)
test, follow the measurement order prescribed by the regula-
tions.
If the CO/HC concentration at 2,500 rpm does not comply
with regulations, try the following procedure.
Race the engine again at 2,500 rpm for approx. 1 minute and
quickly repeat steps 4 and 5 above.
This may correct the problem.

EM–20

–

ENGINE MECHANICAL

Idle and/or 2,500 rpm CO/HC Check

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.

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

Symptoms

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Cause

ÑÑÑÑÑÑ

Normal

ÑÑÑÑÑ

High

ÑÑÑÑÑÑÑÑÑÑÑ

Rough idle

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

1. Faulty ignition:

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Incorrect timing

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Fouled, shorted or improperly gapped plugs

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Open or crossed high–tension cords

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Cracked distributor cap

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

2. Incorrect valve clearance

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

3. Leaky EGR valve

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

4. Leaky intake and exhaust valves

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

5. Leaky cylinder

ÑÑÑÑÑÑ

Low

ÑÑÑÑÑ

High

ÑÑÑÑÑÑÑÑÑÑÑ

Rough idle

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

1. Vacuum leak:

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

(Fluctuating HC reading)

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

PCV hose

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

EGR valve

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Intake manifold

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Air intake chamber

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Throttle body

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

ISC valve

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Brake booster line

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

2 Lean mixture causing misfire

ÑÑÑÑÑÑ

High

ÑÑÑÑÑ

High

ÑÑÑÑÑÑÑÑÑÑÑ

Rough idle

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

1. Clogged air filter

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

(Black smoke from exhaust)

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

2. Faulty EFI system

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Faulty pressure regulator

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Clogged fuel return line

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Defective engine coolant temp. sensor

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Defective intake air temp. sensor

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Faulty ECU

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Fault injectors

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Faulty throttle position sensor

ÑÑÑÑÑÑ

ÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑ

ÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑÑ

Faulty volume air flow meter

–

ENGINE MECHANICAL

Idle and/or 2,500 rpm CO/HC Check

EM–21

COMPRESSION CHECK

HINT: If there is lack of power, excessive oil consumption or
poor fuel economy, measure the compression pressure.

WARM UP AND STOP ENGINE
Allow the engine to warm up to normal operating tempera-
ture.

2. DISCONNECT

DISTRIBUTOR

CONNECTOR

3. DISCONNECT HIGH–TENSION CORDS FROM SPARK

PLUGS (See steps 2 to 8 on pages EM–10 and 11)

4. DISCONNECT

INJECTOR

CONNECTORS

REMOVE SPARK PLUGS (See page IG–8)

CHECK CYLINDER COMPRESSION
(a) Insert a compression tester into the spark plug hole.
(b) Fully open the throttle.
(c) While cranking the engine, measure the compression

pressure.

HINT: Always use a fully charged battery to obtain engine rev-
olution of 250 rpm or more.
(d) Repeat steps (a) through (c) for each cylinder.
NOTICE: This measurement must be done in as short
time as possible.

Compression:

1,226 kPa (12.5 kgf/cm

, 178 psi) or more

Minimum pressure:

981 kPa (10.0 kgf/cm

, 142 psi)

Difference between each cylinder:

98 kPa (1.0 kgf/cm

, 14 psi) or less

(e) If the cylinder compression in one or more cylinders is

low, pour a small amount of engine oil into the cylinder
through the spark plug hole and repeat steps (a) through
(c) for the cylinder with low compression.

•

If adding oil helps the compression, the piston rings
and/or cylinder bore are probably worn or
damaged.

•

If pressure stays low, a valve may be sticking or
seating improper, or there may be leakage past the
gasket.

REINSTALL SPARK PLUGS (See page IG–9)

Torque: 18 N

⋅

m (180 kgf

⋅

cm, 13 ft

⋅

lbf)

8. RECONNECT

INJECTOR

CONNECTORS

9. RECONNECT HIGH–TENSION CORDS TO SPARK

PLUGS (See steps 14 to 20 on pages EM–17 to 19)

10. RECONNECT

DISTRIBUTOR

CONNECTOR

EM–22

–

ENGINE MECHANICAL

Compression Check

TIMING BELT

COMPONENTS

–

ENGINE MECHANICAL

Timing Belt

EM–23

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Lexus SC300 / Lexus SC400. Manual — part 422

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