Make Character to enter backseat of car

Dipper4Real

So I tried to make my very first mod, which will get me a stretch-limo + driver to drive around. I can spawn the car and bring it to my place, but I can't enter it. I tried this in my onTick-Method:

if (Game.Player.Character.GetVehicleIsTryingToEnter() == stretch && isEnteringCar == false)
{
        isEnteringCar = true;
        Game.Player.Character.Task.EnterVehicle(stretch, VehicleSeat.RightRear);
        isEnteringCar = false;
}

isEnteringCar is just a bool that's supposed to make sure, that this method is only executed once while entering. But the problem is, when I press F, my character runs to the right back door and then just stops, while "flimmering". It#s like the "EnterCar"-Animation gets resetted every tick, but I thought the bool would prevent that. So what am I doing wrong?