herrickmky
New Member
- Joined
- Apr 1, 2015
- Messages
- 7
- Car
- W124 300CE-24
Hi, my Merc is a 92 300CE-24 with the M104.980 engine. One of the haunting problems is the high idle and would like to seek your advice.
Three years ago (2019), the idle all of sudden stuck at 1500 rpm. My mechanic tried adjusting the duty cycle without success. It turned out the air potentiometer is faulty. I replaced it with a new Bosch one, the idle was back to normal. After 2 years of poise and quiet idle, the idle problem occurred again and this time it is like this:
Current problem
M104.980 idle problem
Throttle hesitation
It starts at around 1000 rpm, seems normal. However, it rises to 1300-1500 rpm after 1-2 minutes. This symptom happens every time. In case I depress the accelerator and release it, the idle does not return to 1500 rpm but stays at 2000 rpm.
Recently, when I press the accelerator, it hesitates between 2000-3000 rpm, you can see the problem from the video clips, then it goes to higher rpm with no problem
Diagnosis findings
Finding of the diagnosis are as follows:
Parts have been replaced
Since i bought the car in 2014, I replaced the following parts with new with the purpose to fix other issues and to do preventive maintenance
Right before the problem reocurred, the following parts were replaced
Since the problem has come back, the following were done
Three years ago (2019), the idle all of sudden stuck at 1500 rpm. My mechanic tried adjusting the duty cycle without success. It turned out the air potentiometer is faulty. I replaced it with a new Bosch one, the idle was back to normal. After 2 years of poise and quiet idle, the idle problem occurred again and this time it is like this:
Current problem
M104.980 idle problem
Throttle hesitation
It starts at around 1000 rpm, seems normal. However, it rises to 1300-1500 rpm after 1-2 minutes. This symptom happens every time. In case I depress the accelerator and release it, the idle does not return to 1500 rpm but stays at 2000 rpm.
Recently, when I press the accelerator, it hesitates between 2000-3000 rpm, you can see the problem from the video clips, then it goes to higher rpm with no problem
Diagnosis findings
Finding of the diagnosis are as follows:
- Voltage of the air potentiometer is not stable. Every time I restore it to 0.7v, it goes to 1.x v after engine restart
- Duty cycle sticks at 10%, no response to the adjustment regardless CW or CCW turn
- OBD I always indicates Crank Shaft Sensor error
- Throttle value sensor - ok
- Decelerator switch - ok
Parts have been replaced
Since i bought the car in 2014, I replaced the following parts with new with the purpose to fix other issues and to do preventive maintenance
- ICV (I installed another one for testing, no improvement)
- Air potentiometer (To fix the 1st high idle problem. I installed another one for testing this time, no improvement)
- OVP (I installed another one for testing, no improvement)
- EHA valve
- Ignition and HT cable
- Fuel pressure regulator
- Fuel pump and filter
- Crank shaft position senor
Right before the problem reocurred, the following parts were replaced
- Cam shaft adjuster
- Cam shaft position sensor
- Alternator + OAD
- Distributor cap and rotor
Since the problem has come back, the following were done
- Fuel distributor rebuilt
- Clean the throttle valve
- Replaced the air hoses
- Replaced the Decelerator switch (it
- Replaced the coolant temp sensors (The ohm of the one going to the ECU seems much higher than what it should be according to the info I found in this forum, however, I tried both 2 new sensors, they report the same ohm reading)
