Hello,
I'm experiencing an idle control issue with my Mercedes W124 230E (M102 engine, automatic transmission) using the Invent Jetronic ECU (firmware 4.1.6).
The engine starts and runs well, and all ECU input signals appear to be working correctly (Idle switch, vehicle speed signal, coolant temperature, etc.).
The problem occurs when the engine is under load while the car is stationary:
- In Park/Neutral, idle is stable. Target idle is 840 rpm, actual idle is around 940 rpm.
- The ICV duty at normal idle is around 35–40%.
- When I shift into Drive and keep the brake pedal pressed, the ICV duty gradually increases from about 40% to around 55% over approximately one minute.
- If I then shift back to Neutral or Park, the engine speed rises to around 1500 rpm and stays there.
- At this point, the ECU does not reduce the ICV duty below approximately 52%, even though the target idle is still 840 rpm.
- If I manually reduce the ICV duty, the engine speed immediately drops back to normal.
I initially suspected the PID settings, but changing them did not solve the issue:
Original: Kp = 20, Ki = 12, Kd = 25
Tested: Kp = 15, Ki = 8, Kd = 25
The behavior remained exactly the same.
The car does not provide a Drive/Neutral gear position signal to the ECU (only the reverse switch exists on this transmission), so the ECU has no direct gear position input.
My question is:
Is this expected behavior of the idle control algorithm, or could another function (such as idle compensation, anti-stall, idle integrator, or another correction) be preventing the ICV from returning to its normal duty after the transmission load is removed?
I have attached both the calibration (.imf) and the recorded log (.bin).
Any suggestions would be greatly appreciated.
