This week a 07 Toyota Carola was took to my garage for repair. It is very important to communicate with the car owner before you start repairing. So I asked the car owner when did he noticed the problem. According to the car owner, the check engine light on the vehicle suddenly came up, with noises caming from exhaust pipe while accelerating. He also found black stains in the exhaust pipe.
I use an OBD2 tool, Toyota Tester IT2 to pull trouble codes, and troubleshot ignition coil faults and intake air temperature sensor fault. I tried to cleared the fault codes. But the intake air temperature sensor fault just could not be erased. I read the system data flow from the Toyota diagnostic tool and verified there was something wrong with the intake air temperature sensor. Considering that there were black stains in the exhaust pipe, I was afraid that the problem may be caused by bad combustion.
So I disassembled the 4 ingintion coils and the spark plug for further inspection. To my surprise, all the 4 coils were of different length, and the spark plug was seriously burned (I believe many of you can deal with this problem.) According to data from Toyota IT2, the head of the intake air temperature sensor was worn. So I tested the voltage of the sensor with MST-2800B multi-meter, and found that the intake air temperature did not change at all.
I repalced the four ingintion coils, the spark plug and the air flow meter, and deeply clean the oil system, and the problems were then fixed.