Our 1995 Volvo 850 station wagon has started suddenly stalling, then after some period of time we can restart. Last summer it only happened in traffic and would restart almost immediately. The mechanic had it for 3 days and couldn’t reproduce the problem. However, last weekend it suddenly stalled while traveling on the highway at 60 mph and only barely made it to the breakdown lane. Wouldn’t restart over the next 1/2 hour and so was towed to a garage and the keys left in the box. Monday morning, the mechanic finds the car, turns the key…and it starts. He can’t find the problem either. What are the possibilities and how would you test for them?