Not sure why the idea is to jump to replacing the TB. TB issues will throw codes. Typically, so will ICV but a sticking ICV won't always throw codes. And is much more likely to cause weak idle. Low throttle input are also handled by the ICV on the M54 engine.

IMO the first step here should be smoke testing it, and if it passed a smoke test I would remove the ICV, verify correct operation and reinstall it ensuring it is oriented correctly.