2000 Plymouth Voyager • 98,000 miles

When my vehicule îs started and I turn the key Off IT stays on
I have replaced the ignition Smith on IT
January 2, 2013.

It may be deiseling. That is when they is so much carbon depsoits on the pistons that it heats up and acts like a glow plug and ignitets gas fumes and keeps running which pulls more gas in. Unusual for your mileage, a little early but if you use you van in stop and go traffic not a surprise.
I suggest some high quality fuel system cleaner that will remove carbon depsoits and sludge such as BG44K. You will have to go to a car dealership at their parts counter to find it but it is worth it. Nothing else works as well. It is $20 a bottle. I suggest two bottles each in a full tank of gas then run a third tank of gas and see how it does after that. Your oil may get very dirty after this so be prepared to change it.