I have a throttle tip-in stumble that seems fairly common for the M54 engine but in doing research haven't found any smoking guns. Before I open up the parts cannon I wanted a bit of help troubleshooting. Just over 160k miles on the vehicle and pretty much all original except for the stuff I've done.


Just off idle, when trying to accelerate, the engine feels like it bogs down for a split second before it catches. Once it catches, the engine feels healthy.


I've been poking around OBDFusion and INPA for anything obvious. The sample rate is slow for either so its hard to see transients like this, but nothing obviously off with the mass air flow, air intake temp. I also did a smoke check on the intake to check for vacuum leaks and did not find any. Long term fuel trims on both banks is +1.6%. No stored codes.


I've already replaced the plugs and the VANOS seals as I read these can cause similar symptoms, no obvious difference from either. I have not yet replaced the coils, MAF, or O2 sensors.

One thing that seems odd in INPA - checking the PWG/MDK values (the pedal position sensor vs throttle position sensor), intuitively these should roughly be in sync with each other unless I am understanding this system incorrectly. I assume there are redundant sensors for both to measure the driver's desired throttle input and and actual throttle position. the PWG sensors react immediately but the MDK ones barely change. Also, the sensors for each set aren't in sync with each other (i.e the two PWG sensors have an offset, and the MDK sensors appear to be inverted, one reads 0.5 volt and the other reads 4.5 volt). I posted two images, one at no pedal input and the other with some nominal level of throttle input. Does this mean there's something up with my throttle body?


Any help here is appreciated. Oh, also this is one of those rare 5-speeds. Other than the tip in issue it's great fun to drive!

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