Hey smart!
Try disassemlbling the idle valve and throughly clean the carbon out w/ carb cleaner. Replace any dry/cracked rubber hoses that you can get to: Vaccum leaks? I had the same problem w/ my 82 380 prior to rebuilding. Afterwards, the idle is perfect. The control, resolder trick works too...sometimes. If you tap while running, it "may" try to correct itself. Hope this helps! les