My grandma’s Ford Windstar has been smoking at start up. Also a little rough idle on hot starts, but hard to re-create consistently. The van has about 160k mikes and is maintained very well. I checked the compression: 190, 215, 190, 190, 210, 190. The middle two cylinders have very high compression!!! Also, those two spark plugs had heavy/dark fouling, and oil on the threads. What is the most likely culprit? And what should I do??