Symptom
A BMW 735 sedan, when idling after starting, engine speed instability, tachometer pointer teeter, idling obviously hunt.
Analysis and Diagnosis
BMW 735 sedan, equipped with inline 6-cylinder engines, the engine cover is opened the ceremony. For this failure idle instability phenomenon, empirically, we first idle control valve, throttle BMW ICOM A2 position sensor cleaning adjustments did not improve. Test emergency refueling, always felt should foot throttle, which is hard acceleration, the engine speed is not fast with the throttle open and lift,
Slow acceleration but normal; neutral regardless emergency refueling, slow refueling, engine operation can be considered normal, the circuit appears to be normal, because there is no abnormal sound bad, so we use a pressure gauge to measure the hydraulic system operating pressure. When the engine is idling, oil pressure 270kPa, acceleration up 30OkPa; idle deprived pressure regulator on the vacuum tube, the oil also rose to 300kPa; when the return pipe clamp with pliers, hydraulic MB SD Connect C4 exceed 50OkPa, described fuel pump, pressure regulator device, the system pressure were normal. But the car idling car travel, driving hard acceleration working, judging solely from the oil, it is the oil disruption, caused by inadequate supply. There may be a diagnostic nozzle clogging.
Troubleshooting
In the hydraulic system access special injector cleaning machine, one hour after cleaning, loading retest car back to normal idle speed, tachometer pointer stable fixed; out of the test, rapid acceleration performance significantly improved throttle should feet.
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