Is your engine dieseling for some reason? I've heard this term used in relationship to an engine continuing to run even though the key has been removed. I'm sorta sketchy on exactly what causes it, but apparently it is related to improper combustion in the engine which causes "hot spots." I guess these hot spots can make the engine continue to run...

That's all I gotta offer... Sorry. Perhaps contact your mechanic and ask what could cause your engine to randomly start dieseling.