{"model":"mk3","model_name":"MK3 Supra","vehicle":"Toyota Supra A70 (1986.5–1992, 7M-GE / 7M-GTE)","document":"Repair Manual","section":"EM","section_name":"Engine Mechanical","page":19,"pages_in_section":98,"title":"Troubleshooting","section_header":"Engine Mechanical — Idle and/or 2,500 rpm HC/CO Concentration Check Method","ocr_text":"Troubleshooting\n\nIf the HC/CO concentration does not comply with regulations, perform troubleshooting in the order given below.\n\n1. Check oxygen sensor operation.\n   (See page FI-139)\n\n2. See the table below for possible causes, and then inspect and correct the applicable causes if necessary.\n\nHC | CO | Symptoms | Causes\n\nHigh | Normal | Rough idle | 1. Faulty ignition:\n                              • Incorrect timing\n                              • Fouled, shorted or improperly gapped plugs\n                              • Damaged or loose high-tension cords\n                              • Cracked distributor cap\n                            2. Incorrect valve clearance\n                            3. Leaky EGR valve\n                            4. Leaky intake and exhaust valves\n                            5. Leaky cylinder\n\nHigh | Low | Rough idle | 1. Vacuum leak:\n         (Fluctuating HC reading) | • Vacuum hose\n                                    • EGR valve\n                                    • Intake manifold (Air intake chamber)\n                                    • Throttle body\n                                    • ISC valve\n                                    • Brake booster line\n                                  2. Lean mixture causing misfire\n\nHigh | High | Rough idle | 1. Restricted air filter\n          (Black smoke from exhaust) | 2. Faulty EFI system:\n                                        • Faulty pressure regulator\n                                        • Clogged fuel return line\n                                        • Faulty air flow meter\n                                        • Defective water temp. sensor\n                                        • Defective air temp. sensor\n                                        • Faulty ECU\n                                        • Faulty injector\n                                        • Faulty cold start injector\n                                        • Faulty throttle position 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