I have a 1985 Volvo 250 wagon with 88000 miles on it. It runs like a champ at low outside tempertatures, but when it's over 75° outside the car will occasionally stall while driving. Even on the highway at high speeds it will bog out and stall. When it stalls it is difficult to immediately restart but given a few minutes it does. When I get it started again I get a loud, high pitched squeal that lasts about 20 seconds. It will run again but eventually stalls again. Any ideas?