I tried clearing the DME adaptations but did not notice any difference. I also went ahead and checked my fuel pressure, 54 psi when pump is running, 48 psi when pump shuts down. I understand 54 psi is the specification so this checks out.


Based on my understanding of the idle air system, the IAC allows air into the manifold up until it reaches 100% duty cycle, then the throttle begins to open.
Total speculation but it feels like this handoff is maybe not happening in a smooth manner. Like you said, maybe the throttle is a bit lazy or slow or there's something weird going on with the IAC. Unfortunately these are both expensive parts and I would be buying OE grade parts (the throttle body is $217 at Rockauto).


I wish I knew what this setup was supposed to feel like when new. There are a lot of complaints of similar symptoms for other M54 powered vehicles on the 3-series and 5-series forums.