Check that your EGR system is working properly by applying a vacuum to the EGR valve and the engine should slow down and maybe even stall.
My engine had a clean EGR but what fixed it was new Oxygen Sensors, spark plugs and wires. (Believe it or not, COPPER Champion plugs fixed it when platinum Motorcraft plugs caused very bad running).
Another indication that your engine is running lean is that the temperature will fluctuate more than normal. For instance, after a freeway run, the temperature will rise quite a bit. On my Duratech, the temperature is normally at or below the "N", of Normal. It goes up in traffic to the "O".
When my O2 sensors and plugs were causing a misfire and pinging, the temperature would go higher, more often.
For some reason, the engine can run quite poorly without any check engine light coming on.
- Randall
