A 2010 TOYOTA car with a mileage of about 103 thousand km. The owner reflected that the vehicle was not running well when it was cold, and it started after about 7~8 times. The engine started abnormal noise after starting. Fault analysis: the vehicle to the store inspection, the engine top like the valve to send "click" sound, abnormal sound as the engine speed increases, to 1300 to 1800r/min sound most obvious. Check engine control system, no failure code appears, normal. The suspicion is that the valve clearance is too large. The valve chamber cover is removed and the valve clearance is checked. It is found that the intake and exhaust valves are not abnormal in the range. After the customer agrees, the cylinder head is removed and checked. It is found that the top of the 2-3 cylinder piston has a trace of interference with the intake valve near the intake door side. Dismantling the cylinder head is difficult to extract when disassembling the 2-3 cylinder valve, and finds that the 2-3 cylinder intake valve stem and the intake valve seat are attached with a large amount of gum. In this case, the failure point is found. Because the valve's sliding in the tube is not smooth, the valve can not be completely reset by the elastic force of the valve spring, and the valve is forced to reset the valve to cause the abnormal response when the piston goes up. The cause of this failure should be poor fuel quality, excessive gum production after combustion, and impeding the sliding of valves. Troubleshooting: remove the valve completely and clean the cylinder head and solve the problem after loading. Failure revelation: an example of engine failure due to poor fuel quality is not uncommon. Customers should be constantly reminded to go to regular gas stations. Fault review: bad fuel oil damage to the car! In addition to vehicles, the interests of victims and the credibility of maintenance stations are being tested.