Many times it is caused by carbon build-up in the cylinders. The carbon becomes hot enough to ignite the unburt fuel that is still in your cylinders after you shut the key off. A too rich fuel mixture can cause this condition.

sowsear46, its good to have another Panhandler on the 'Bolt. Next time I drive through Hale Center, you will have to show me your truck.

Phil

Never hold your farts in. They travel up your spine and into your brain...that is where crappy ideas come from.