Re: Misfire Blues
Obviously, in the 150 K miles on your engine, the valve clearance has never been adjusted. That maintenance procedure should have been done a very long time ago,and you are lucky that the engine runs at all. Over time and miles, the exhaust valves tighten up and don't allow enough exhaust out of the cylinders for efficient combustion of each new cycle of each cylinder. At the same time, the intake valve adjustment becomes looser which further upsets the balance of fuel/air mixture in the cylinder. Miss-fires occur when there is an imbalance of fuel and air for each combustion stroke of the engine. Too much fuel, with too much old exhaust from the previous cycle, and not enough air, the spark plug won't ignite the charge in the cylinder, and/or the combustion is incomplete and can't deliver the usual amount of force to keep the engine running smoothly.
But don't take my word for it- see a mechanic and get the job done. You are only about 100 K late.