Inspect Cohc

(a) Start the engine.

(b) Run the engine at 2,500 rpm for approximately 180 seconds.

(c) Insert the CO/HC meter testing probe at least 40 cm (1.3 ft) into the tailpipe during idling.

(d) Immediately check the CO/HC concentration during idling and/or at 2,500 rpm.


• Complete the measurement within 3 minutes.

• When carrying out the 2 modes (idling and 2,500 rpm) test, the measurement orders are prescribed by the applicable local regulations.

(e) If the CO/HC concentration does not comply with regulations, troubleshoot in the order given below. (1) Check the heated oxygen sensor operation.







- Incorrect timing

- Fouled, shorted or improperly gapped plugs

2. Incorrect valve clearance

3. Leaky intake and exhaust valves

4. Leaky cylinders



Rough idling (Fluctuating HC reading)

1. Vacuum leaks:

- PCV hoses

- Intake manifold

- Throttle body

- IAC valve

- Brake booster line

2. Lean mixture causing misfire



Rough idling (Black smoke from exhaust)

1. Restricted air filter

2. Plugged PCV valve

3. Faulty EFI systems:

- Faulty pressure regulator

- Faulty engine coolant temperature sensor

- Faulty mass air flow meter

- Faulty ECM

- Faulty injectors

- Faulty throttle position sensor

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