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A car with a mileage of about 180 thousand kilometers, using a 4 L V6 engine and a model 1GR of TOYOTA Prado 4 LVX. User response: the engine's idle speed jitter, acceleration is weak, engine fault lights are lit. Fault judgement: read the fault code with the decoder, showing that the relative position of the camshaft is wrong (column 2). According to the analysis of fault code hints, the possible causes include timing error, timing control valve failure, Holzer sensor phase fault, mixture gas concentration, combustion bad, three element catalytic blockage and so on. Following the basic inspection of the vehicle, after the dismantling, it is found that the 2 side cylinder spark plugs are obviously burning bad, and the data of the data flow are in the basic range, so the 6 spark plugs are replaced first, and the normal time regulating valve of the column 1 and the column 2 are exchanged between them, and the fault appears again after a moment and appears the same. Like the fault code, the engine idling jitter is still. When the engine front cover is disassembled, when the crankshaft is rotated, it is found that there is a loose and tight phenomenon during the rotation of the 2 sides of the camshaft chain, and the disassembly of the timing chain finds that the tensioner has been damaged. Change the damaged column 2 timing chain, chain tensioner, middle wheel, after the installation of the test, the engine jitter disappeared; but after a while the engine trouble light again light, read the fault code, showing: the camshaft relative position error (column 1). Had to disassemble and check the column 1 again, check the timing chain, check the camshaft position sensor signal disc. After checking, the camshaft signal disc is installed correctly. So where is the problem? It is possible that the chain tensioner damage in front of the first 2 leads to the loosening of the chain, which makes the gas phase of the engine column 2 deviate, so that repeated movement will lengthen the timing chain of the column 2, while the column 2 chain will also have an impact on the chain of column 1. The 1 chain of positive time and the new chain of column 2 are dismantled, and the two and the root chain are put together to make a comparison. It is found that the chain of column 1 is not the same as the new chain length of column 2, which is nearly 4 mm, indicating that the chain of column 1 is also damaged partly. So the chain, the tensioner, and the middle wheel of the list 1 have been damaged. At this point, the timing chain, the chain tensioner, and the middle wheel of column 1 and column 2 are replaced. (the timing chain of column 1 is mainly damaged by the influence of column 2). After loading, test run, idle speed is steady, speed up smoothly, fault lights are no longer lighted, and the trouble is completely eliminated.