Stalling in hot weather-ok when not hot

The stalling condition with your 1998 Chevrolet Express Van may be do to a low idle condition caused by a dirty throttle body. If you are not sure about the idle speed you may need a qualified technician to help you decide if the idle speed is now lower than it used to be. If it turns out the base idle is low, removing the air cleaner and air intake and cleaning the throttle body and throttle plate using brake cleaner or carburetor cleaner may take care of your low idle and stalling.