1999 Plymouth Voyager The engine wouldn't shut off!

Do you have a remote car starter installed?
If your not sure look for an antenna usually above the rear view mirror

these aftermarket starter can cause all kinds of problems and have seen them do this exact thing many times before

if it does have one unplug it these are always found under the dash on the left(drivers side) will be a black box that might just be stuffed in around the colum or if it was install properly will be secured with tie straps

I don't have a remote car starter installed. Just a regular old turn the key; it doesn't even have a keyless entry fob. A friend suggested the gas and oxygen mix is running too rich in the carburation system (?) Is time for a new gas filter maybe?

I appreciate your reply. My ex used to take care of my vehicle, and it's challenging to try to stay on top of it myself.