Page text (OCR transcript)
Troubleshooting
If the HC/CO concentration does not comply with regulations, perform troubleshooting in the order given below.
1. Check oxygen sensor operation.
(See page FI-139)
2. See the table below for possible causes, and then inspect and correct the applicable causes if necessary.
HC | CO | Symptoms | Causes
High | Normal | Rough idle | 1. Faulty ignition:
• Incorrect timing
• Fouled, shorted or improperly gapped plugs
• Damaged or loose high-tension cords
• Cracked distributor cap
2. Incorrect valve clearance
3. Leaky EGR valve
4. Leaky intake and exhaust valves
5. Leaky cylinder
High | Low | Rough idle | 1. Vacuum leak:
(Fluctuating HC reading) | • Vacuum 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. 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 ECU
• Faulty injector
• Faulty cold start injector
• Faulty throttle position sensor