Fault diagnosis: 1) first use HDS to read the engine fault code and show that everything is normal. 2) remove the ignition coil, spark plug and control circuit for inspection without any suspicious faults. 3) use fuel pressure gauge to detect fuel pressure of 320kPa, within normal technical range. 4) as the engine just trembled at idle speed, the throttle body was removed from another vehicle for replacement. 5) turn on the ignition switch to check the voltage of the 4 injectors is 12V, indicating that the injector power supply is normal. 6) remove the injector for inspection, found that the fourth cylinder injector is relatively damp, indicating that the fuel injector has leakage or abnormal fuel injection. 7) in the fourth cylinder injector line series a LED test lamp, and plug the plug, and then start the engine, the engine is normal starting, but after the ignition switch off, the fourth cylinder LED lights still flicker, indicating that the 4 cylinder control line and ECM/PCM has a fault. 8) after careful inspection, the fuel injector and the control circuit are unlikely to fail, so replace ECM/PCM and troubleshooting. Maintenance summary: because of abnormal ECM/PCM control of the fourth cylinder injector, the fuel injector is not regularly injected, and the fuel consumption is increased.