@Brian_Evans so all you really did was adjust the idler tension?
Yeah that sounds stupid but yeah.
Yeah I had the same problem recently. For me it was after moving from 3mm to 1.75mm. With 3mm this doesn’t ever happen.
I have the same problem using 3mm extruding to 0.5mm, and have stripped the head down to components and soaked the metal parts over night in a sealed container of isopropanol. This helped to reduce the issue but think the main cause is the head is not heating up evenly and therefore causing this issue. I have some more testing to do and will update if I fine more answers.
Thanks for all of the help and feedback on this everyone, I haven’t had a chance to implement the changes yet, but will try to do that tonight and let you know the results.
I had that problem when my thermister went bad. Temps jumped around about 20 degrees during printing. Swapped my hotend, and all good now.