TL;DR:
Swapped Z4 E85 (M52TUB28 with MS45 ECU) worked fine for months, then started going into limp mode randomly with fluctuating idle (1100-1400 RPM) and error codes like P1635 (Throttle Valve Adaptation not adapted). Replaced throttle body twice (used parts), but the issue keeps returning.
• Suspected grounding issue; replaced engine ground cable—no change.
• CCV is worn (makes noise) and will be replaced, along with deteriorated intake elbow (no visible leaks).
• Post-cat O2 sensor error, but it shouldn’t affect performance.
• Read that MS45 ECUs can fail and cause random errors due to memory issues.
Still looking for the root cause.
Hello
,
The car is a Z4 E85, the engine has been swapped to an M52TUB28, while retaining the intake and all the electrical components from the original M54B25 engine, including the MS45 ECU, with no modifications.
Everything worked perfectly for a few months, until the car started randomly going into limp mode (both at idle and while driving), lighting up multiple warning lights on the dash—Check Engine, EML, traction control—and the idle fluctuating wildly between 1100-1400 RPM. Again, this happened completely at random and would fully resolve after several restarts.
Once the first symptom appeared, it started happening more and more frequently, but without any pattern that I could identify to understand what was causing it.
Most of the time, it threw the following code:
P1635: Tire / Axle Ratio Out of Acceptable Range
Throttle Valve Adaptation; Lower Mechanical Stop Not Adapted
Throttle Valve Adaptation; Lower Mechanical Stop Not Adapted
So, I thought the throttle body was faulty and replaced it with a used one from a parts car.
Everything worked fine again for a few months while I enjoyed the car, and all of a sudden the problem started happening again.
I figured, okay, the replacement was probably worn out as well, and I just had the bad luck of it failing, so I bought another throttle body, again from a parts car. (Tbh, at this point I’m starting to suspect that the TB might not actually be the root cause of the issue)
This time, after only a few weeks, the problem reappeared, just like before and it drives me crazy.
In the past, I had issues with the engine ground, so I thought that might be the cause, and I installed a new ground cable from the chassis to the engine, so I don’t think it’s a grounding problem.
All time cleaned the ICV valve and the TB.
My CCV is a bit worn and seems to be making some strange noises. I’ve already ordered a replacement along with all the hoses, but could the CCV really cause these kinds of errors? Maybe an air leak or something, I’m not sure.
I’ve also ordered the rubber elbow between the throttle body and the MAF sensor, which is quite deteriorated, although there are no signs that it’s leaking air.
In addition to that, I also have an error on one of the post-cat O2 sensors, which I’ve also ordered. However, as far as I know, the post-cat lambda sensors shouldn’t affect the engine’s in any way.
What I’ve also read is that these ECUs eventually fail, where they can no longer read certain parts of their memory and start throwing random errors like this.
2796, 281C, 2806, 281D, 2806, 28B3
(Almost all with “Pending fault present, Validated fault has been present during this drive cycle” status”)
Please help.
Swapped Z4 E85 (M52TUB28 with MS45 ECU) worked fine for months, then started going into limp mode randomly with fluctuating idle (1100-1400 RPM) and error codes like P1635 (Throttle Valve Adaptation not adapted). Replaced throttle body twice (used parts), but the issue keeps returning.
• Suspected grounding issue; replaced engine ground cable—no change.
• CCV is worn (makes noise) and will be replaced, along with deteriorated intake elbow (no visible leaks).
• Post-cat O2 sensor error, but it shouldn’t affect performance.
• Read that MS45 ECUs can fail and cause random errors due to memory issues.
Still looking for the root cause.
Hello
,The car is a Z4 E85, the engine has been swapped to an M52TUB28, while retaining the intake and all the electrical components from the original M54B25 engine, including the MS45 ECU, with no modifications.
Everything worked perfectly for a few months, until the car started randomly going into limp mode (both at idle and while driving), lighting up multiple warning lights on the dash—Check Engine, EML, traction control—and the idle fluctuating wildly between 1100-1400 RPM. Again, this happened completely at random and would fully resolve after several restarts.
Once the first symptom appeared, it started happening more and more frequently, but without any pattern that I could identify to understand what was causing it.
Most of the time, it threw the following code:
P1635: Tire / Axle Ratio Out of Acceptable Range
Throttle Valve Adaptation; Lower Mechanical Stop Not Adapted
Throttle Valve Adaptation; Lower Mechanical Stop Not Adapted
So, I thought the throttle body was faulty and replaced it with a used one from a parts car.
Everything worked fine again for a few months while I enjoyed the car, and all of a sudden the problem started happening again.
I figured, okay, the replacement was probably worn out as well, and I just had the bad luck of it failing, so I bought another throttle body, again from a parts car. (Tbh, at this point I’m starting to suspect that the TB might not actually be the root cause of the issue)
This time, after only a few weeks, the problem reappeared, just like before and it drives me crazy.
In the past, I had issues with the engine ground, so I thought that might be the cause, and I installed a new ground cable from the chassis to the engine, so I don’t think it’s a grounding problem.
All time cleaned the ICV valve and the TB.
My CCV is a bit worn and seems to be making some strange noises. I’ve already ordered a replacement along with all the hoses, but could the CCV really cause these kinds of errors? Maybe an air leak or something, I’m not sure.
I’ve also ordered the rubber elbow between the throttle body and the MAF sensor, which is quite deteriorated, although there are no signs that it’s leaking air.
In addition to that, I also have an error on one of the post-cat O2 sensors, which I’ve also ordered. However, as far as I know, the post-cat lambda sensors shouldn’t affect the engine’s in any way.
What I’ve also read is that these ECUs eventually fail, where they can no longer read certain parts of their memory and start throwing random errors like this.
2796, 281C, 2806, 281D, 2806, 28B3
(Almost all with “Pending fault present, Validated fault has been present during this drive cycle” status”)
Please help.
