93 240 volvo sedan

I have had this car since it was new. The car is well maintained and has just over 100,000 miles. My question is this: in hot weather only, (I live in Maine) the car following multiple stops and starts (when I run several errands) will not start…I turn the key, all the lights on the dashboard come on, the car will not start. If I wait for a minimum of 45 minutes, the car will turn over and run like a champ. This will happen occasionally and a long period of time will pass when it does not happen, and then it happens again. Once this event occurs the same thing can occur within several days of the first occurence…has never occured except in summer months Volvo specialists have looked at this car and no one can tell me what this might be