@MIC97 Go to mods > update > update.rpf > x64 > levels > gta5. You should see this "popgroups.ymt". If you wan't add-on cars or peds to spawn automatically, you will have to edit this file. Extract the file to anywhere you want and edit it.
Use CTRL + F to search for the term "vehGroups" without the quotes. You will see the group "VEH_POOR".
For an example if you want to add an add-on car, do this;