I have some horrible pre-igniton with my engine. I have tried the whole sea foam thing and what not. It only happens when i turn my car off. Sometimes it never stops and i have to just start the car back up again. Could this happen because of a high idle? What am I missing?

could be a combo of high base idle, ignition timing too far advanced, and excessive engine temp

the temp is fine, but i still have to check my timing and fix the idle