Hey Steve,


From looking at your readings, I would go looking for vacuum leaks. Flush your cooling system, but don't run straight water for any length of time since it will start to cause corrosion very quickly. Check the thermostat, it may need to be replaced. Try washing the radiator from the fan side with water spray to clean any debris blocking airflow. Also, you may need to replace the airbox thermostat. Its a thermally actuated spring that controls the flow of air from the cool side behind the radiator or the hot side from the heat stove on the exhaust manifold. These fail in the hot air position, and the constant stream of hot air is bad for the air mass sensor and engine operation. FCP Groton (www.fcpgroton.com) has these for less than $10.00. As mentioned earlier, a new oxygen sensor may be a good idea. Get a Bosch sensor, they are the best quality and longest lasting. Replacing the spark plugs is a good start, but the Platinum +4 plugs are unnecessary in these engines. Ordinary NGK copper plugs work great in these engines. Check the rest of your ignition system, cap, rotor, wires. Check the ignition timing if its adjustable. Make sure the flame trap and its plumbing are in good shape, this can be a source of vacuum leaks. If your catalytic converter is original, it may be getting tired by 251k. FCP groton, Eeuroparts, and other places have them. I don't think the octane rating of the gas will make much difference.

Good luck with your emission inspection.


Regards, Jon 'Uncle Olaf'