1997 850. Purchased this vehicle about 4 months ago. Temperatures have begun to rise in Kansas this past week, days averaging 90+. Noticed last Saturday morning (about 90 degrees at the time) the Service Engine light come on for about 1/2 mile of driving then goes out. Checked hoses, listened for airleaks, etc., and other obvious things but didn't see or hear anything notable. Didn't come on any more on Saturday. Sunday, same thing, light came on duruig morning idle, went out after I drove about 1/2 mile again. Now whenever I turn the car off and recrank, it reoccurs and still goes out after 1/2 mile of driving. Thought it might be oxygen sensor (do not have maintenance records, so it's hard to tell when it was last -- if ever -- changed). Any ideas on where to begin diagnosing would be greatly appreciated.