EM-14 ENGINE MECHANICAL — Idle HC/CO Concentration Check Method 4. RACE ENGINE AT 2,500 RPM FOR APPROX. 2 MINUTES 5. I NSERT HC/CO METER TESTING PROBE INTO TAIL PIPE AT LEAST 40 cm (1.3 ft) 6. MEASURE HC/CO CONCENTRATION AT IDLE Wait at least one minute before measuring to allow the concentration to stabilize. Complete the measuring within three minutes. If the HC/CO concentration does not conform to regula- tions, see the table below for possible causes. Troubleshooting HC CO Problem Cause High Normal Rough idle 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 High Low Rough idle (Fluctuating HC reading) 1. Vacuum leak: • PCV hose • EGR valve • Intake manifold • Air intake chamber • Throttle body • ISC valve • Brake booster line 2. Lean mixture causing misfire High High Rough idle (Black smoke from exhaust) 1. Restricted air filter 2. Faulty EFI system • Faulty pressure regulator • Clogged fuel return line • Defective water temp. sensor • Defective air temp. sensor • Faulty ECU • Faulty injector • Faulty cold start injector • Faulty throttle position sensor • Air flow meter