If it's dieseling it shouldn't be because of the timing because the spark plugs aren't firing with the key off. Dieseling is usually caused by a hot spot in one or more cylinders, often a glowing bit a carbon. Here is a short, simple explanation.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.