I am currently trying to diagnose a 2000 Lincoln LS with 74000 miles for a missfire and here is what I have came up with. Vehicle is intermittenly missing a idle and under a load with the check engine light on. I have ran a computer test with snap-on scanner. The codes are not consistent. After retrieving the codes I would clear them and test drive the vehicle again until the light sets. Most of the time it was on immediately after the next start up. The codes I have gotten were idle circuit fault (IAC motor or circuit) every time,random missfire once,#6 and #7 cyl. missfire once, cmp circuit fault(camshaft position sensor) once and the last time only idle circuit. You could still feel the car missing and even on the data stream it was not showing a miss???!!! Now all of these were giving at different times and none were the same twice.(except the idle curcuit) I even switched the #6 with #5 to verify a faulty coil,but nothing. I also read about the oil in the spark plug hole,but how much oil does it take to affect them. (only have a small trace and some on the plug treads) All new boots and motorcraft platinums. Need Info Bad!!!!!!! Also the customer ran the vehicle out of fuel and seemed to notice the problem worse after refueling.