There are 2008 TOYOTA Highlander with a mileage of about 198 thousand km. Customer response: the engine jitter is more and more serious recently. It was slightly jitter. Now it is more obvious. It is also not very well accelerated, and the fuel consumption is also high. First of all, it is confirmed that the fault phenomenon is about 1200r/min of the engine speed, the idle speed jitter is obvious, the test speed is not good enough, and the breathing is trembling. Fault diagnosis: use the diagnostic instrument to detect the trouble free code of engine and transmission. For detecting data streams, the sum of short-term and long-term fuel correction values is 1.5% normal, and the sum of two columns is 20.3%, just larger than the 20% threshold value. Number 2 oxygen sensor voltage 0.03V also shows thinning. Because of the engine jitter, the two column system is thinning, so the analysis may be the leakage of the two column system or the two row of the injector, so the injector is removed and cleaned and the amount of fuel injection is detected. The injector is good. Use the carburetor cleaner to check the leakage and spray to the injector and the intake manifold, and no air leakage is found. Is the vacuum tube leakage? When the vacuum lines are removed, they are stopped at the junction of the gas manifold ends. The engine has no change, indicating that the PCV and the vacuum pipelines are also normal. Use the current test to cut off the injection of each cylinder, see if there is a lack of cylinder phenomenon, there is no obvious difference in each cylinder; use the fuel pressure gauge to check the fuel pressure 320kPa, the normal value of 310 ~ 340kPa. At the same time, two cylinder pressures are checked. Why is it that the diagnostic test is sparse and the speed is high? Is there a problem with VVT? Use the current test from 128% to 127% to see the angle of the VVT entry system, see its change angle, VVT intake and exhaust control changes according to the target angle. According to the maintenance manual test VVT oil control valve at - 12 8% of the engine did not change, at 127% when the engine idle jitter or even stall, indicating that the VVT control system and operation is normal. By this time, the maintenance went to a deadlock. Did ECM fail? Because a column of fuel correction values in the normal range, so did not check, analysis whether a series of failures and the impact of the two column, in order to prevent misjudgment or return to the origin, the engine is inspected in the same line as above, the engine first cylinder pressure (a series of cylinder pressure (a column) during the inspection process. One cylinder is low, the problem should be the fault caused by the insufficient pressure of the first cylinder of the engine. When the engine is removed and checked, it is found that the inlet valve of the first cylinder of the engine has a lack of one angle, which causes the air leakage of one cylinder, which is the cause of the high engine speed, and the engine is normal after the valve is replaced. Fault summary: from the above inspection data, one column appears to be normal, but the air leakage of one column of air leads to the increased intake of two columns and the two column system is dilute, so the data flow in the maintenance process is important, but the data flow will also mislead the direction of maintenance, to prevent the misjudgment, or to press the requirement. The item is inspected in an all-round way.