[raycow]

I have never before heard the term "cadillac" used to describe what I think you are talking about. Does the engine continue to run (very roughly, and with loud splitting or cracking noises) after you turn off the switch? If yes, this is usually caused by carbon (or other deposits) building up in the combustion chamber and being heated to the point where it serves as an ignition source.

This is not a timing issue, because, if you think about it, there is no spark with the switch off. If the engine is idling faster than normal, it couldn't hurt to reduce the idle speed and see if that helps. The next step would be to pull the plugs and see what they have growing on them. If they look bad, a plug change MIGHT make the problem go away for a while. If nothing else works, you will have to pull the heads and clean out the offending deposits.

If you have a manual transmission, it is a lot less work to just put it in gear and engage the clutch with the engine idling and your foot on the brake. It is a real problem only if you have an automatic, because then you have no easy way of killing the engine.

Ray