Went to search engine and keyed in "300E idle". Came up with this:

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=378566&sortby=lastpost&sortorder=descending

Lots of possibilities. Find a shop versed in "diagnosis" and not parts replacement. An hr. or two of shop labor by way of a good tech should get to the heart of the matter.

Good luck.