Stock '82 Plymough Gran Fury, 318/904 and Demon StreetDemon 1901 carb (Thermoquad clone). Car runs very well normally, but if ambient temp outside is more than 70*F, then after fully warming up it will idle at approx. 2-300 rpm low and rough, and eventually stall out unless I keep a foot on the brake and slightly open the throttle to keep the RPMs up. Vacuum gauge reads steady, and car accelerates with no stumbling or other issues. Any idea on the problem? Mixture and timing are adjusted fine, no apparent vacuum leaks (18" solid/steady at curb idle). Ignition is stock electronic ignition with a NAPA box, stock electronic ignition distributor is hooked up to ported vacuum.