Previous owners neglect, and possibility of mechanic not doing their job, when I bought the car it was fine 116,000 miles developed a slight misfire wanted the injectors changed, apparently they got changed then it came back with a new issue with the airmass meter gone, I don't know how a car goes in fromjectors and comes back with the airflow mass meter broken but never mind, 4 hours in the clear with the injectors done but still was misfiring I had to warm it up before driving it, and then it happened about 14,000 miles later, running like an old tractor, took oil cap off and boom you can see it not holding pressure, I spend a few grand on prevention, but if you don't physically do it yourself you can't trust