NOTE: This check method is used only to determine whether or not the idle HC/CO complies with regulations. PRECHECK INITIAL CONDITIONS (a) Air cleaner installed (b) Normal engine operating temperature (c) All pipes and hoses of air intake system connected (d) All accessories switched off (e) All vacuum lines properly connected NOTE: All vacuum hoses for EGR systems, etc. should be properly connected. (f) EFI system wiring connectors fully plugged (g) Ignition timing set correctly (h) Transmission in N range (i) Tachometer and HC/CO meter calibrated and at hand MEASUREMENT 1. RACE ENGINE AT 2,500 RPM FOR ABOUT 2 MINUTES 2. INSERT TESTING PROBE OF HC/CO METER INTO TAILPIPE AT LEAST 40 cm (1.3 ft) 3. 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 your regulations, see the table below for possible causes. TROUBLESHOOTING HC | CO | Symptoms | Causes High | Normal | Rough idle | 1. Faulty ignition: • Incorrect timing • Fouled, shorted or improperly gapped plugs • Open or crossed ignition wires • Cracked distributor cap 2. Faulty EGR system: • EGR valve 3. Leaky exhaust valves 4. Leaky cylinder High | Low | Rough idle Fluctuating HC reading | 1. Vacuum leak: • Vacuum hose • Intake manifold 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 • Faulty air flow meter • Defective water temp. sensor • Defective air temp. sensor • Faulty ECU • Faulty injector • Faulty cold start injector • Faulty throttle position sensor