Toyota Supra 1990 Manual page 51

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ENGINE MECHANICAL -

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

Troubleshooting

If the HC/CO concentration does not comply with regula-

tions, perform troubleshooting in the order given below.

Check oxygen sensor operation.

(See page FI-119)

See the table below for possible causes, and then inspect

and correct the applicable causes if necessary.

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

1. Vacuum leak:

(Fluctuating HC reading)

Intake manifold (Air intake chamber)

Throttle body

Brake booster line

2. Lean mixture causing misfire

1 . Restricted air filter

(Black smoke from exhaust)

2. Faulty EFI system:

Faulty pressure regulator

Clogged fuel return line

Faulty air flow meter

Defective water temp. sensor

Defective air temp. sensor

Faulty injector

Faulty cold start injector

Faulty throttle position sensor

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