The engine was designed for a different fuel and 100LL was just coming into
use when the POH was written. Plug fouling wasn't on the radar screen.
--
Roger Long

What is the recommended idle speed listed in the POH?

If the recommended idle speed results in aircraft movement when idling
with
brakes off, does the POH address the issue?

This just sounded like something the manufacturer might be aware of and
have
some recommendations for...